Abstract: A device for administering a fluid product includes a first housing part with a receiver for the product, a second housing part detachably connectable to the first housing part, a piston rod held such that it can be displaced for the exertion of an emptying movement, an actuatable or releasable drive element for the piston rod, a coupling element including a coupling input element that couples the drive element to the piston rod in a coupling engagement, transmits a driving force of the drive element to the piston rod, and triggers the emptying movement, and a decoupling element displaceably connected to the second housing part and coupled to the first housing part such that it is displaced, by a movement of the housing parts in relation to each other when the housing parts are separated into a decoupling position wherein the piston rod is decoupled from the coupling input element.

Abstract: A drug injection device includes a last dose setting having a main drive pin, a drive wheel, a driven wheel, an abutment element fixedly coupled to, or integrally formed with, the driven wheel. The drive wheel has a rotation axis parallel to a longitudinal axis and is configured to be driven about the longitudinal axis by a knob and to be periodically driven in rotation about the rotation axis by the main drive pin, during a drug dose setting. The driven wheel has a second rotation axis parallel or coaxial to said longitudinal axis and is configured to be periodically driven about the longitudinal axis by the drive wheel. The abutment element is configured to prevent the rotation of the drive wheel about the longitudinal axis when the knob has made a predetermined number of full and/or partial rotations about the longitudinal axis correlated to the predetermined drug volume.

Abstract: The present invention relates to a finger grip (1) arranged to be connected to a syringe barrel having a plunger and a plunger rod for driving said plunger. The finger grip comprises a body having a lower side with finger supporting surfaces (13) for supporting fingers of a user during handling and an engagement member (5) being moveable between an inactive position where the engagement member is arranged not to engage with the plunger rod of the syringe barrel and an active position where the engagement member is arranged to engage with a grooved surface on the plunger rod of the syringe such that feedback is given to a user as the plunger is moved relative to the finger grip. An activation member (7) for moving the engagement member from said inactive position to said active position is built-in into the finger grip.

Abstract: An apparatus is disclosed, comprising a detector unit comprising a detector configured to detect an actuation action performable via the detector unit to an actuation button of a medical device to cause the medical device to eject at least a portion of a medicament comprised in the medical device. The detector is configured to detect the actuation action based on a detection of a force and/or a touch applied to the detector unit as part of the actuation action. The apparatus further comprises an electric unit connected to the detector and configured to store and/or provide information related to the detected actuation action. Furthermore, an according method and a computer program for controlling this method are disclosed.

Abstract: An injection device is disclosed including a housing assembly defining a pair of ramps and adapted to hold a medicament cartridge. A driver is adapted to advance the piston within the cartridge. A plunger having a pair of arms is moveable between a retracted position and an advanced position. Each of the arms are engageable with a respective one of the ramps as the plunger is advanced. A braking mechanism may include braking members on the arms and braking tracks proximate the ramps. Excessive force exerted on the plunger may flex the arms and engage the braking members with the braking tracks. The plunger arms may be connected together by a material bridge that biases the plunger arms apart from each other. The arms may include detents that engage to prevent the arms from moving due to the biasing force of the material bridge when the arms are in the fully retracted position.

Abstract: A drug injection device includes a housing with a cartridge having a predetermined drug volume, a dose setting mechanism for setting a drug dose, and a dose delivery mechanism. A dose setting service element rotates about a longitudinal axis during the drug dose setting. The dose setting mechanism has a last dose setting device to prevent setting of a drug dose greater than the drug volume remaining in the cartridge. The last dose setting device includes a pinion coaxial with the longitudinal axis that rotates about the longitudinal axis with the dose setting service element during drug dose setting, and a rack engaged with the pinion that moves parallel to the longitudinal axis when the pinion rotates. The pinion and the rack have mutual abutment elements that prevent further rotation of the pinion after the rack has travelled an axial length correlated to the predetermined drug volume.

Abstract: A drive mechanism for a drug delivery device having a rotationally fixed plunger rod driven by a lead screw. The lead screw engages a free lock which is coupled to a release knob. A dose setting dial cooperates with an inner cylinder using a clutch to establish the axial movement of the plunger rod during dose setting and dispensing.

Abstract: An assembly for a drug delivery device is provided, the assembly comprising a feedback feature. The feedback feature is configured to indicate an end of the dispense operation to a user by giving an audible and/or tactile feedback.

Abstract: A plunger sub-assembly (40, 60, 70; 80) for a pre-filled medicament injector for expelling a dose of a medicament, comprising: a) a container (60) holding a medicament, the container (60) comprising a body (61) with a proximally facing rim surface (64), and a distally slideable piston (63); b) a plunger (40); and c) a tolerance compensating element (70; 80) configured to cooperate with the plunger (40) and to cooperate with either the proximally facing rim surface (64) or the piston (63), the tolerance compensating element (70; 80) being rotatable relative to the plunger (40) to adjust the piston (63) end of dose position. The plunger sub-assembly (40, 60, 70; 80) is formed so that end of dose state occurs by the plunger (40) cooperating with the proximally facing rim surface (64). Pre-filled medicament injectors and methods of assembling a pre-filled medicament injector are further described.

Abstract: A dispensing mechanism for delivering a dosage of medicament including a housing, a push button, a crank arm that is slideably engageable with the push button, a ram, and a ratchet gear releasably engageable with the crank arm and ram, translation of the push button along an axis causing the crank arm to engage and rotate the ratchet gear which causes the ram to distally advance relative to the housing.

Abstract: A dose setting mechanism for a medicament delivery device, which dose setting mechanism comprises, a tubular member 10 having a longitudinal track 18 of a predetermined length; a dose drum 40, coaxial with the tubular member 10, and being axially and rotationally movable relative to the tubular member 10; a stop member 90, axially movable but rotationally locked relative to the tubular member 10, and further being in an axially slaved connection with the dose drum 40; wherein said stop member 90 comprises a track follower 98 in engagement with the longitudinal track 18, such that rotational movement of the dose drum 40 relative to the tubular member 10 may cause a maximum axial displacement of said dose drum 40 and said stop member 90, relative to the tubular member 10, corresponding to said predetermined length.

Abstract: A dose setting mechanism for a drug delivery device is disclosed. The mechanism comprises an outer housing and an inner housing having an external groove and a helical spline. The inner housing helical spline guides a driver to dispense a set dose. A dial sleeve is disposed between the outer and inner housing and is rotatably engaged with the inner housing. When a dose is set, the dial sleeve is rotated and translates away from both the outer housing and the inner housing.

Abstract: Auto-injector for administering a dose of a liquid medicament includes a housing to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end with an orifice to apply against an injection site. A spring means, upon activation, can push the needle from inside the housing through the orifice and past the proximal end, operate the syringe to supply the dose of medicament, and retract the syringe with the needle after delivering the medicament. An activating means can lock the spring means in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring means for injection.

Abstract: A syringe is disclosed. The syringe comprises a plunger and a barrel. The plunger can be rotated relative to the barrel to lock, unlock and/or translate the components relative to each other.

Abstract: Disclosed herein are delivery devices for delivering a volume of a drug product, placebo product, or other product including a fluid. The devices may include a barrel having a longitudinal axis, a proximal end region, and a distal end region. The proximal end region may include an opening, and the barrel may be configured to receive a drug therein. A plunger rod may be disposed at least partially inside the barrel and protruding from the opening. The plunger rod may include a rack having a plurality of teeth. The device may further include a pinion having a plurality of teeth configured to engage with the plurality of teeth of the rack, and rotation of the pinion against the rack may move at least a part of the plunger rod along the longitudinal axis of the barrel.

Abstract: A dosing device for an injection device, the dosing device including an actuating element for adjusting and/or dispensing a dose from the injection device, a thrust element for generating a forward movement for discharging a dose and a coupling to which the actuating element and the thrust element are coupled such that a rotational movement of the actuating element is transmitted directly to the thrust element and an axial movement of the actuating element is different than an axial movement of the thrust element.

Abstract: An assembly for a medication delivery device, wherein the assembly is configured to perform a dose setting operation, the assembly having a dose setting sleeve and a drive sleeve, wherein the dose setting sleeve has a first dosing track having a first length and defining a first size of a dose and a second dosing track having a second length and defining a second size of a dose, wherein the first length is different from the second length and the first size is different from the second size. The drive sleeve has an engagement feature configured to engage with one of the dosing tracks. The assembly is configured such the dose setting operation has a first step wherein the engagement feature is aligned with one of the dosing tracks and a second step wherein the engagement feature is moved along the dosing track.

Abstract: A sensing system for determining a zero position of a medication delivery device. The sensing system includes at least one actuator member, a biasing member, a stop surface and a sensor. The stop surface is structured and arranged within the device housing for abutment by a push surface of the at least one actuator member as a screw element of the device screws to a zero position from a dosing position. The abutment forces the at least one actuator member to move relative to the screw element from a first position to a second position against a resistance provided by the biasing member. A sensor within an electronics module is adapted to recognize the at least one actuator member at the second position.

Abstract: An injecting device includes a housing having a longitudinal axis extending. A dose setting member is rotatable in the housing in a first or second direction about the longitudinal axis. A plunger extends through a bore of the dose setting member and into a bore of a barrel engaged with the housing. Pushing on an arm extending through a slot in the housing rotates the dose setting member in the first direction. As it rotates, indicia on the dose setting member are progressively displayed through an aperture in the housing. An actuator is engaged to release the dose setting member to rotate in the second direction and this rotation causes the plunger to move axially within the barrel's bore and push the pre-set dose of fluid therefrom. The dose setting member remains in a constant axial position within the housing during rotation in each of the first and second directions.

Abstract: An injection device having a drive member with first and second gear patterns that are fixed relative to each other. The drive member is rotatable and translatable in first and second opposing axial directions. A plunger expels medicament from a cartridge when it is translated in an advancing direction. A dosage indicator indicates a set dosage. A first gearing arrangement operably couples the first gear pattern with the plunger wherein rotation of the drive member in a first direction translates the drive member in a first axial direction without movement of the plunger and translation of the drive member in the opposite axial direction drives the plunger in the advancing direction. A second gearing arrangement operably couples the second gear pattern with the dosage indicator and moves the dosage indicator to indicate an increase in the set dosage when the drive member is translated in the first axial direction.

Abstract: The present disclosure relates to an administration mechanism for a medicament delivery device having a movable sleeve, and a delivery member cover having a distal end portion configured to receive the movable sleeve. The delivery member being configured to be linearly displaceable between a first position and a second position relative to the movable sleeve, wherein the distal end portion has an end face defining a guide surface and the movable sleeve has a radially outwards extending first follower structure configured to cooperate with the guide surface when the delivery member cover is moved from the first position towards the second position, causing the movable sleeve to rotate.

Abstract: The invention relates to a system having a dosing dispenser for dispensing pasty or viscous material with a housing, a cartridge displaceably accommodated therein and a walking piston accommodated in the cartridge that forms a unit ready for assembly with a shutter button to be arranged at a cartridge end.

Abstract: A drug delivery device comprising a case adapted to hold a medicament container, a plunger disposed within the case and slidable from a proximal position into a distal position for delivering a medicament from the medicament container, an audible indicator that is arranged within a case pocket lateral to the plunger and that is in operative connection with the plunger, the audible indicator comprises at least one indicator spring and at least one locking element. The indicator spring is biased by the locking element, and the indicator spring relaxes due to a release of the locking element by a movement of the plunger.

Abstract: A drive mechanism for an injection device for setting and dispensing of a dose of a medicament includes an inner body fixable inside a housing of the injection device, the inner body including an elongated shaft extending in an axial direction. The elongated shaft includes an outer thread and a blocking structure on an outer circumference. The drive mechanism includes a tubular-shaped display member having an inner thread engaged with the outer thread of the inner body, a dose member axially displaceable between a dose setting position and a dose dispensing position relative to the inner body, and a blocking sleeve axially fixed to the dose member, rotationally fixed to the display member and including at least one blocking element to axially engage with the blocking structure to block an axial displacement of the dose member from the dose setting position towards the dose dispensing position.

Abstract: Bodily fluid collection systems are described where the system may be used for collecting and transferring sperm into a syringe. The syringe is configured to have a distal collection tip which is gently tapered or radiused to present a smooth and atraumatic surface and which is specifically configured and shaped to be inserted within and received by the collection receptacle. The distal collection tip has a shape which corresponds directly to a tapered reservoir defined at the bottom of the collection receptacle such that a distal opening defined through the tip is optimally positioned within the concentrated bodily fluid pooled within the reservoir for collection. Moreover, the gentle taper of the collection tip may present an atraumatic surface for inhibiting damage to the sperm contained within the ejaculate as the sperm is suctioned into the distal opening for insemination into the female.

Abstract: The invention relates to an autoinjector for dispensing a liquid product, in particular a highly viscous medication, comprising: a housing, a product container, which is arranged in the housing and has a slidable piston, wherein the piston can be slid in a dispensing direction in order to dispense the product contained in the product container, a forward drive element, which acts on the piston as the product is being dispensed, a first spring, which is preloaded such that the product can be dispensed from the product container by the sliding of the forward drive element and the piston, and a rotation element, which is operatively coupled to the forward drive element, wherein the first spring acts on the rotation element in such a way that the rotation element is set into rotation in order to dispense the product, wherein the rotation element or the forward drive element has a thread having a variable pitch.

Abstract: A syringe comprising: a body delimiting a chamber; a piston able to slide in the chamber of the body along a longitudinal axis of the syringe, wherein the piston comprises a rod, a head, and a finger rest, which are all in one piece; and a deformable retention device designed to prevent the piston from leaving the body entirely, wherein the retention device is force-fitted in the chamber, extends around the piston over an angular sector strictly greater than 180° when it is in the assembled position, and has protruding external ribs which extend parallel to the longitudinal axis and are plastically deformable when the retention device is assembled in the chamber.

Abstract: An assembly includes a clutch member and a drive member movable relative to one another between a first relative position and a second relative position, in the first relative position, the clutch member and/or the drive member is rotatable relative to a housing, in the second relative position, the deflectable feature is arranged to prevent rotation of the clutch member and/or of the drive member relative to the housing, and wherein the deflectable feature and the interaction feature are arranged such that, when the clutch member and the drive member are moved relative to one another from the first relative position into the second relative position, the deflectable feature and the interaction feature mechanically interact in order to deflect the deflectable feature.

Abstract: A dispensing mechanism for delivering a dosage of medicament including a housing, a push button, a crank arm that is slideably engageable with the push button, a ram, and a ratchet gear releasably engageable with the crank arm and ram, translation of the push button along an axis causing the crank arm to engage and rotate the ratchet gear which causes the ram to distally advance relative to the housing.

Abstract: The mechanism includes a body, a drive member movable in the body, a main spring that is loaded when a dose is set and is released for moving the drive member during a delivery of a dose, and a movable trigger inhibiting a movement of the drive member, a movement of the trigger releasing the main spring and the drive member. The trigger is moved from a start position to an end position relative to the body during a setting of a dose, the end position having a distance from the start position that increases as the dose set increases.

Abstract: The drive mechanism comprises a lead screw and a lead screw nut, which are aligned with an axis. The lead screw has screw threads having the same pitch and being intertwined.

Abstract: A PIVC includes a catheter adapter having a catheter that extends distally from the catheter adapter, and an introducer needle that inserts through the catheter. The introducer needle has a grip component at a proximal end of the introducer needle. The grip component extends outwardly and distally to form a winged grip adjacent the catheter adapter when the introducer needle is inserted within the catheter. The grip component can be rotatable within the catheter adapter to allow repositioning of the winged grip with respect to the catheter adapter.

Abstract: An injection pen (1) includes a housing (2), a lead screw (75), a dose set member (6), a setback member (17), and a rotatable driver (60). The lead screw (75) is axially moveable in the housing (2). The dose set member (6) is connected to the housing (2) for dose setting and dose correcting. The setback member (17) is operatively connected to the dose set member (6). The rotatable driver (60) is operatively connected to the setback member (17) and the lead screw (75). The driver (60) is prevented from rotating during dose setting and dose correcting, and the driver (60) rotates during an injection to axially move the lead screw (75).

Abstract: An injection pen (1) includes a housing (2), a lead screw (75), a dose set member (6), a setback member (17), and a rotatable driver (60). The lead screw (75) is axially moveable in the housing (2). The dose set member (6) is connected to the housing (2) for dose setting and dose correcting. The setback member (17) is operatively connected to the dose set member (6). The rotatable driver (60) is operatively connected to the setback member (17) and the lead screw (75). The driver (60) is prevented from rotating during dose setting and dose correcting, and the driver (60) rotates during an injection to axially move the lead screw (75).

Abstract: An assembly for a drug delivery device is provided, wherein the assembly comprises an actuator which is configured to perform a setting movement in order to set a dose and which is configured to perform a dispense movement in order to dispense a dose and a piston rod which is configured to be moved in a distal direction in order to dispense a dose, and a snap feature which is configured to snap into engagement with the piston rod. The snap feature may be configured to inhibit a dispense movement of the actuator and/or a setting movement of the actuator when a maximum amount of medication has been delivered.

Abstract: The disclosure is directed to a differential gear mechanism for a drug delivery device with a primary drug delivery assembly and a secondary drug delivery assembly, wherein the primary drug delivery assembly comprises a primary dose dial sleeve and wherein the secondary drug delivery assembly comprises a secondary drive sleeve. The disclosure is also directed to a respective drug delivery device.

Abstract: The present invention relates to a drive mechanism which is suitable for an injection device, especially a pen type drug delivery device. The mechanism includes a housing, a dosing member which during dose setting, dose resetting and dose dispensing rotates relative to the housing between a zero dose position and a maximum dose position, and an insert that is rotationally constrained to the housing. The dosing member and the insert each include at least one abutment feature contacting each other when the dosing member reaches its zero dose position during dose dispensing, and an audible and/or tactile feedback is generated by the contact of the abutment features.

Abstract: Assembly for a drug delivery device and drug delivery device An assembly for a drug delivery device (1) is described comprising an activation member (6A) adapted and arranged to be axially moved in a delivery direction for triggering a dose delivery operation of the assembly, a first interaction member (17) and a second interaction member (18) which are adapted and arranged to mechanically cooperate with one another during a dose delivery operation of the assembly and to be rotated with respect to one another during the dose delivery operation, wherein the assembly is configured such that movement of the activation member (6A) in the delivery direction brings the interaction members (17, 18) into mechanical contact for generating a friction between the interaction members (17, 18), wherein an amount of friction controls a relative rotational speed of the interaction members (17, 18) during a dose delivery operation. Furthermore, a drug delivery device comprising the assembly is described.

Abstract: A drug delivery device adapted to receive a cartridge and comprising a housing, an expelling assembly with a threaded piston rod, a threaded nut and a drive element arranged in non-rotational engagement with the piston rod, a drive coupling actuatable between a resetting state in which the piston rod can be moved proximally, and an operational state in which the drive element can drive the piston rod distally, wherein the drive element and the threaded nut are not moved axially relative to the housing when the drive coupling is actuated.

Abstract: A drive mechanism for a drug delivery device includes an elongated housing extending in an axial direction and a piston rod to operably engage with a piston of a cartridge to displace the piston in an axial distal direction. A drive sleeve is rotatably supported in the housing, operably releasable from the piston rod for setting of a dose, and operably engageable with the piston rod for dispensing of the dose. A dose limiting member is engaged with the drive sleeve and engaged with the piston rod in such a way that it is displaced in axial direction relative to the drive sleeve when the drive sleeve rotates relative to the piston rod during a dose setting procedure. At least one stop is configured to engage with the dose limiting member for limiting the axial displacement of the dose limiting member during the dose setting procedure and to impede further displacement of the drive sleeve relative to the piston rod.

Abstract: An automatic injector includes a housing having a guide, a drive control mechanism, a transmission assembly, a motor, and an energy source. The housing may further include a cartridge cover. A drive control mechanism includes a drive screw, a cartridge carrier, a plunger carrier, and one or more control transfer instruments, such as a puck or cylinder. The drive screw interfaces and connects with the plunger carrier. The automatic injector is configured to accept a variety of syringes as cartridges for drug delivery. The cartridges may be ejected from the injector and safely disposed after use, making the injector a reusable automatic injector. The reusable automatic injector may further include one or more sensors, such as a cartridge sensor and a patient sensor.

Abstract: A handheld injection device includes a housing and a dose indicator positioned within and axially constrained to the housing and rotatable with respect to the housing during dose setting and during dose dispensing. The dose indicator includes a flexible clicker arm which, only during dispense, is displaced in a first radial direction and, when the device reaches its minimum dose position, in a second, opposite radial direction.

Abstract: A drug delivery device, comprises a housing having a longitudinal axis; an axially moveable component that is moveable along the longitudinal axis between a dose dialing position and a dose delivery position when a user operates the device to deliver a dose of drug; an encoder sleeve; an encoder pattern provided on the encoder sleeve, the encoder pattern comprising relatively conductive portions and relatively non-conductive portions that together comprise coded information; a contact-supporting component; and plural electrical contacts provided on the contact-supporting component. The plural electrical contacts contact the encoder pattern when the dose delivery button is in the dose dialing position and wherein the device is configured to move the contact-supporting component relative to the encoder sleeve as the axially moveable component moves from the dose dialing position to the dose delivery position such as to move the electrical contacts into positions where they do not contact the encoder pattern.

Abstract: Flush syringe assemblies capable of creating pulsatile movement of the plunger rod as it moves in the distal direction within a syringe barrel, while preventing overpressurization of the cathether are provided. An exemplary flush syringe assembly includes a syringe barrel with a first pulsing element and a chamber with flush solution, a plunger rod with a stopper and a second pulsing element that interacts with the first pulsing element to provide an engagement force that causes pulsatile movement of the plunger rod and a thumb press slidably attached to the plunger rod with a pulse control element. The pulse control element is compressible to create a compression force that is greater than the engagement force of the first pulsing element and the second pulsing element.

Abstract: The present invention relates to an injection device for automatic spring driven injection of a liquid drug. The injection device has a dose setting mechanism by which doses of an individual size can be set by a user, and a mechanical dose size display for displaying the size of the set dose. The scale drum (20) is coupled to a rotatable dose dial button (10) which is axially retained in relation to the housing (2) and by which the individual doses can be set.

Abstract: The present invention relates to a torsion spring based automatic injection device for apportioning set doses of a liquid drug and which injection device is provided with an End-of-Dose feedback mechanism providing a user with an audible signal once the set dose has been injected. During injection, the scale drum rotates back to its “zero” position under influence of the torsion spring. This rotation is halted shortly before reaching the “zero” position by stopping means. The scale drum is thereafter only allowed to continue rotation and thus reach the “zero” position once the torque applied to the scale drum by the torsion spring surpasses a threshold value.

Abstract: A medication delivery device having a housing having a proximal and a distal end, a medication receptacle designed to be engaged with the distal end of the housing by engagement of a first engagement feature with a second engagement feature and a dosing mechanism. The dosing mechanism includes a piston rod which is rotatable and moveable in a distal direction for medication delivery and a drive device for moving the piston rod in the distal direction for medication delivery. The medication receptacle includes an actuation element that brings a guiding element in a guiding position. The guiding element guides the piston rod for medication delivery. The first engagement feature and the second engagement feature are moveable into engagement by a movement of the medication receptacle which ends in a rotational movement without axial movement of the medication receptacle with respect to the housing.

Abstract: An assembly for a drug delivery device is disclosed. An example assembly includes a housing, a rotation member, a drive member, and at least one correction member. The rotation member is adapted to be rotated with respect to the housing in a first rotational direction for delivering a dose of a drug. The drive member is coupleable to the rotation member for delivering the dose. In a delivery mode, the drive member and the rotation member are coupled such that the drive member follows rotational movement of the rotation member in the first rotational direction due to mechanical interaction of the rotation member and the drive member. In a correction mode, the rotation member and the drive member are decoupled such that the rotation member is rotatable in the first rotational direction with respect to the drive member.

Abstract: The present artificial insemination instrument may include a single use, hollow, elongate, metal pipette and a single disposable syringe that is not toxic to bovine sperm. The apparatus is used with any type of diluent that is not toxic to bovine sperm. In various embodiments, a technician may use non-sorted reduced sperm count semen straws from a bull stud, cut an unsorted semen straw into several pieces to use one piece at a time per cow, thaw one straw and mix the non-sorted semen with diluent, or use reduced sperm count semen straws filled with sex sorted semen by the manufacturer. A procedure is disclosed to use the artificial insemination instrument, reduced sperm count semen from any of the aforementioned sources, a non-toxic syringe, and a diluent to achieve conception rates at least as good as conventional prior art device and procedure conception rates.

Abstract: A syringe comprising: a body delimiting a chamber; a piston able to slide in the chamber of the body along a longitudinal axis of the syringe, wherein the piston comprises a rod, a head, and a finger rest, which are all in one piece; and a deformable retention device designed to prevent the piston from leaving the body entirely, wherein the retention device is force-fitted in the chamber, extends around the piston over an angular sector strictly greater than 180° when it is in the assembled position, and has protruding external ribs which extend parallel to the longitudinal axis and are plastically deformable when the retention device is assembled in the chamber.