Abstract: An exploratory shaft-making apparatus creates a vertical hole down into a geological formation while sending a payload into the vertical hole. The apparatus includes a metallic cylindrical casing; a hollow, conical head section; a payload body; and shaped charges of high explosive below the payload body. The shaped charges are adapted to sequentially detonate starting with the bottom-most shaped charge. The detonation of each shaped charge is configured to create a void space in the geological formation below the casing. The void space permits gravity to move the remaining shaped charges and the payload body atop them to slide downward so that the next shaped charge to detonate is positioned below the bottom end of the metallic cylindrical casing. A shock absorbing material may be included in the head section. The payload body optionally has a removable cap. A lift fitting may be attached to the payload body.

Abstract: A energy transfer device (10) is provided that is capable of transferring the energy output from one pyrotechnic device (52) to another device (78) for initiating firing thereof. Device (10) comprises a device housing (12) in which a deformable device insert (14) is received. Device insert (14) comprises a central passageway (34) for transmitting the output from a pyrotechnic device (52), including energy, gasses, and/or solids, to another pyrotechnic device (78). The passageway (34) conducts the pyrotechnic device output to a precise location on the second pyrotechnic device (78) where firing is most effectively initiated. The energy transfer device (10) may be employed as a part of a tool (44) used in well completion operations.

Abstract: A line charge system includes a sock with a series of explosive sections and a detonation cord attached to each explosive section. A pair of spaced tubes made of explosive material are disposed about the line and secured to the explosive material of each section resulting in a hinged connection between each explosive section and the detonation cord.

Abstract: An auxiliary cartridge for use in rock breaking is disclosed which comprises an elongate body, an end closure at each end of the body and a charge of combustible material in the space defined by the body and the end closures. One of the end closures includes a frangible membrane which closes off a charge of combustible chemicals. On being subjected to the pressure of an external ignition of fast burning combustible material, the membrane fails and permits flame to flash through it from externally of the auxiliary cartridge to internally thereof thereby to ignite said charge.

Abstract: A breaching device for non-explosively cutting through a substrate, such as the leg of an offshore oil platform or other large cylinder from within the leg or large cylinder. The device includes a ring and a plurality of Reactive Material (RM) feed assemblies. Each RM feed assembly is arranged around the ring and includes an extendible nozzle. Each RM feed assembly includes a cavity that may contain RM that when ignited exits the nozzle. The nozzles are spring loaded and arranged to extend toward the inner surface of the substrate to be cut when the ring is rotated and/or oscillated. This arrangement results in a substantially uniform cut of the substrate from within with much less danger, material, equipment and cost than is currently required to remove large water-based structures.

Abstract: A breaching device that may be used to create a linear and, if desired, continuous, cut or breach in a metal structure. The cut or breach created may be non-linear in shape and not deviate from the functionality of the device. The device includes a plurality of containers joined together, such as by a metal wire or the like to form a series of cutting charges. One or more of the containers includes Reactive Material (RM) that may be ignited electronically or some other activation mechanism. The containers that do contain RM are sealed with the RM therein and preferably fabricated to be sufficiently heat resistant so that the RM is only ignited intentionally. The RM that is contained in the containers may be fired simultaneously, sequentially or in a programmed pattern, depending on the requirements of the application.

Abstract: A downhole tool gun string assembly comprises a first perforating gun operable to generate a first pressure at a first location in a wellbore, wherein the first perforating gun comprises a first plurality of perforating charges; a second perforating gun operable to generate a second pressure at a second location in the wellbore, wherein the second pressure is different from the first pressure and the second perforating gun comprises a second plurality of perforating charges, and wherein at least one of the second plurality of perforating charges is operably associated with a secondary pressure generator, where the first perforating gun and the second perforating gun are configured to maintain a pressure at a selected location in the wellbore below a threshold when the first and second perforating guns are activated substantially concurrently.

Abstract: Pyrotechnic charges that include an explosion generator and an explosive having an outer surface divided into n segments, each segment having kq multiple ignition points for the explosive, k and q being integer numbers greater than 1. The kq multiple ignition points for the explosive are linked by ignition lines forming, for each segment, at least two interleaved partial networks for synchronous ignition of the kq multiple ignition points, each of the partial synchronous ignition networks being linked to a respective partial network detonator.

Abstract: A breaching device that may be used to create a linear and, if desired, continuous, cut or breach in a metal structure. The cut or breach created may be non-linear in shape and not deviate from the functionality of the device. The device includes a plurality of containers joined together, such as by a metal wire or the like to form a series of cutting charges. One or more of the containers includes Reactive Material (RM) that may be ignited electronically or some other activation mechanism. The containers that do contain RM are sealed with the RM therein and preferably fabricated to be sufficiently heat resistant so that the RM is only ignited intentionally. The RM that is contained in the containers may be fired simultaneously, sequentially or in a programmed pattern, depending on the requirements of the application.

Abstract: An apparatus and method for selectively varying the yield of an explosive device is provided. The apparatus generally comprises a main charge that may selectively be consumed and/or detonated to achieve the selected yield ranging from about 0% to about 100%.

Abstract: A perforating gun assembly for use in a wellbore. The perforating gun assembly includes a carrier gun body and a charge holder disposed within the carrier gun body. A plurality of shaped charges are supported within the carrier gun body. A secondary pressure generator is operably associated with at least one of the shaped charges. The secondary pressure generator optimizes the wellbore pressure regime immediately after detonation of the shaped charges by controlling the dynamic underbalance created by the empty gun chambers to prevent excessive dynamic underbalance which may detrimentally effect the perforating operation.

Abstract: A perforating gun, according to one or more aspects of the present disclosure, comprises a loading tube and a plurality of charges mounted in the loading tube with at least a portion of the plurality of charges being tilted relative to an axis of the loading tube. Wherein the plurality of tilted charges are tilted relative to the axis to create a selected reactive dynamic force on the perforating gun to counter a detrimental force on the perforating gun in response to detonation of the plurality of charges.

Abstract: A downhole propellant gas generator includes a propellant assembly that comprises a plurality of individual lengths of an energetic material packed in a selected configuration and at least one initiator. A method for creating a pressure pulse includes igniting an initiator, wherein the one or more initiators are packed with a plurality of individual lengths of an energetic material in a propellant assembly; igniting the plurality of individual lengths of the energetic material subsequent to the igniting of the one or more initiators. A method for stimulating a well includes disposing in the well a propellant gas generator having a propellant assembly that comprises a plurality of individual lengths of an energetic material, and at least one initiator packed among the plurality of individual lengths of the energetic material; igniting the at least one initiator, which in turn ignites the plurality of individual lengths of the energetic material.

Abstract: Explosive apparatus has at least two cuboid moldings, which each includes at least one firing hole and explosive, and whose edge lengths have a ratio of substantially 1:2:4, and a container including an internal area having a square outline and at least one aperture hole to the internal area, the internal area having a side length corresponding at least approximately to a longest edge length of the moldings and a height corresponding at least approximately to a shortest edge length of the moldings or to an integer multiple thereof, wherein the moldings are placed in the internal area of the container such that the at least one firing hole in one of the at least two moldings is aligned with the at least one aperture hole in the container, the aperture hole being intended for insertion of an explosive capsule into the firing hole of the corresponding molding.

Abstract: A detonating device includes a high explosive portion comprising high explosive; a low explosive portion comprising low explosive; and a transition portion between the high explosive portion and the low explosive portion, wherein the transition portion comprises a mixture of high explosive and low explosive.

Abstract: A blasting cartridge comprising an elongated sleeve extending along an axis A and having a first end and a second end; the first end has a first sleeve closure with an opening for holding a detonator; the second end has a second sleeve closure; a space is provided between the first sleeve closure and the second sleeve closure for holding a blasting explosive; wherein the second end is provided with a connector means for releasably connecting the second end of the cartridge with a first end of an adjacent cartridge and comprising a firing pin means for impinging upon a detonator in the first end of the adjacent cartridge when the blasting explosive is detonated by actuation of the detonator in the first end of the cartridge.

Abstract: A loading tube for use in a perforating gun is disclosed which eliminates the necessity for utilization of plastic jackets to restrain shaped charges. The loading tube comprises a first tubular member and an engagement structure in the first tubular member in which the primer ends of the shaped charges may be installed. These engagement structures may be a center plate or inner tubular members. In each of the disclosed embodiments, a detonating cord connects the primer ends of the shaped charges which are installed in the loading tube.

Abstract: A blasting cartridge comprising an elongated sleeve extending along an axis A and having a first end and a second end; the first end has a first sleeve closure with an opening for holding a detonator; the second end has a second sleeve closure; a space is provided between the first sleeve closure and the second sleeve closure for holding a blasting explosive; wherein the second end is provided with a connector means for releasably connecting the second end of the cartridge with a first end of an adjacent cartridge and comprising a firing pin means for impinging upon a detonator in the first end of the adjacent cartridge when the blasting explosive is detonated by actuation of the detonator in the first end of the cartridge.

Abstract: A marker for use in a blasting system which includes a harness, the marker including a control unit, a memory in which information is stored and a connector for connection to a selected location on the harness whereby, upon receipt of an enabling signal via the harness, the information is made available by the control unit.

Abstract: A device for perforating and fracturing a formation in a single trip includes shaped charges and a volume of a gas generator. When activated by detonation of the shaped charges, the gas generator forms a high-pressure gas, which includes steam, that expands to stress and fracture the formation. Suitable gas generating materials include hydrates and hydroxides. Other materials that can be employed with the gas generator include oxidizers and material such as metals that increase the available heat for the activation of the gas generator.

Abstract: A downhole propellant gas generator includes a propellant assembly that comprises a plurality of individual lengths of an energetic material packed in a selected configuration and at least one initiator. A method for creating a pressure pulse includes igniting an initiator, wherein the one or more initiators are packed with a plurality of individual lengths of an energetic material in a propellant assembly; igniting the plurality of individual lengths of the energetic material subsequent to the igniting of the one or more initiators. A method for stimulating a well includes disposing in the well a propellant gas generator having a propellant assembly that comprises a plurality of individual lengths of an energetic material, and at least one initiator packed among the plurality of individual lengths of the energetic material; igniting the at least one initiator, which in turn ignites the plurality of individual lengths of the energetic material.

Abstract: Explosive apparatus having at least two cuboid mouldings, which have at least one firing hole, composed of explosive material, whose edge lengths have a ratio of 1:2:4 and having a container (1) with at least one aperture (80) to an internal area (60) with a square outline, whose side length corresponds at least approximately to the longest edge length of the moulding, and whose height corresponds at least approximately to the shortest edge length of the moulding, or to an integer multiple of this. The mouldings can be placed in the internal area (60) of the container (1) such that at least the firing hole in one of the mouldings is aligned with the aperture (80) in the container (1), and the aperture (80) is intended for introduction of an explosive capsule into the firing hole of the relevant moulding.

Abstract: Disclosed is a device and method for externally perforating a well-bore casing. The perforating apparatus is attached to the outside of the casing itself and is conveyed along with the casing when it is inserted into the well bore. The perforation is accomplished using two groups of charges which are contained in protective pressure chambers which are arranged radially around the outside of the wellbore casing. The pressure chambers form longitudinally extending ribs which conveniently serve to center the casing within the well bore. One group of charges is aimed inward in order to perforate the casing. A second group is aimed outward in order to perforate the formation. In an alternative embodiment, only one group of bi-directional charges is provided.

Abstract: A high energy gas fracturing device, adapted to be lowered into a well. The device comprises a closed tube made of strong material, sized to fit into the well and having at least one sidewall, which defines a set of openings. A set of closure elements seal the openings in a water-tight manner. Also, a charge of propellant is located in the closed tube, the charge achieving best performance if kept dry. Finally, an ignition element contacts the charge.

Abstract: A system and method for making and using a multi-point initiation explosive device that produces an enhanced pressure wave for severing tubing, pipe or casing in an oil or gas well. At least two opposed initiators initiate a column of explosive material from opposite ends, thereby generating opposing pressure waves propagating toward a midpoint between the initial initiators. A shaped-charge assembly with a liner located at the midpoint initiates immediately prior to the arrival of the opposing pressure waves and forms a fast moving jet to pre-score the target pipe prior to the arrival of the pressure pulse propagating from the initial detonations.

Abstract: A system for fracturing wells uses a primary propellant charge to initially produce pressures within the well in excess of the maximum fracture extension pressure of the surrounding formation, but below that which would cause damage to the well. A supplemental propellant charge burns for a substantially longer period of time than the primary propellant charge, and thereby maintains pressures within the well in excess of the maximum fracture extension pressure for a significant period of time following completion of the primary propellant burn.

Abstract: The invention relates to a perforating device comprising one or more perforating gun (1) installed in a perforating body (9), a perforating gun head (2) in the uppermost end of the perforating body (9), a perforating gun base (7) in the lowermost end of the perforating body (9) and a detonating device (3) installed inside or outside the perforating head (2), in which a charge frame (10, 22) is installed inside of the perforating body (9). A plurality of perforator unit connected each other by a detonating cord (15) are provided on the charge frame (10, 22). Every perforator unit comprises an explosive box (11) in a charge socket, a charge (13) in charge housing (12) and energy-bearing media (14). Moreover, an energy-bearing media sleeve (28) is provided outside of the perforating device. The perforating device is easy to manufacture with low cost and can be used securely in the operation.

Abstract: Disclosed is a casing conveyed perforating apparatus and method for externally perforating a wellbore casing. The perforating apparatus is attached to the outside of the casing and is conveyed along with the casing when it is inserted into the wellbore. The perforation is accomplished using two groups of charges, which are contained in protective pressure chambers. Each pressure chamber is positioned radially around the outside of the wellbore casing. The pressure chambers form longitudinally extending ribs, which conveniently serve to center the casing within the wellbore. One group of charges is aimed inward in order to perforate the casing. A second group is aimed outward in order to perforate the formation. In an alternative embodiment, only one group of bi-directional charges is provided.

Abstract: The present invention is an improvement in the design of a perforating gun to perforate the casing in oil and gas wells. Perforating guns have a cylindrical body member with explosive charges at specified intervals designed to shoot outwardly through the body member, the well casing, cement sheath, and into the rock formation. Continuous faceted cuts in the vessel covering the greater part of the circumference, at the level of the charge, serve to reduce the outward distortion of the body member beyond the original diameter of the body member. Reducing the distortion serves to insure that the perforating gun can be removed from the well after the explosive charges have fired.

Abstract: A firing head for a perforating gun includes a detonating block having a first end and a second end, with the second end being structured and arranged so as to be located adjacent to a detonation material. A central passage extends through the detonating block from the first end to the second end. A detonator is located and restrained in the passage so as to be adjacent to the detonating material. At least one venting passage extends from the central passage to an exterior of the detonating block.

Abstract: A perforating device having a longitudinal axis comprising: a loading tube having an explosive charge; a first layer slidable, non fixedly, and removeably disposed over the loading tube; and at least one outer layer in fixed engagement over the first layer and wherein the outer layer is a solid structure.

Abstract: A technique includes arranging perforating charges of a perforating gun into groups of adjacent perforating charges. Each perforating charge of each group is aligned in a direction associated with the group. The groups are oriented to form a phasing for the perforating gun.

Abstract: A tubular charge holder assembly for a perforating gun made of a tube having a plurality of pairs of diametrically opposed openings. The pairs of openings are formed over a length of the tube, wherein the each pair has a larger and a smaller opening. A shaped charge is located within the pairs of openings in the tubular charge holder so that at least a portion of the rim of a front face of the shaped charge extends out of the larger opening and at least a portion of a rear face of the shaped charge extends out from the smaller opening of the tube. A detonating cord is helically wrapped around the outside surface of the tube such that the detonating cord is positioned so that the cord is proximate to the rear surface of each of the shaped charges installed within the tube. A substantially semi-circular clip is positioned on the outside surface of the tube proximate each of the shaped charges.

Abstract: A control system for controlling the initiation of detonation of a series of explosive charges (13) spaced apart from each other in boreholes (12) formed in a rock medium (10) to be blasted, said system being operative to apply controlled time difference in the time interval between successive detonations of at least one phase of the series of charges, and which includes at least three successive detonations, so as to reduce the probability of consecutive stimulation and amplification of ground vibration by reason of the detonation of the charges in the rock medium.

Abstract: A smoke-generating projectile has a decomposable effective mass, the mass including a quick-burning deception component for generating spontaneous smoke, and a slow-burning concealment component for generating persistent smoke. The projectile includes an igniter, an ejection charge and/or ignition decomposition charge and at least one ignition delay device. The projectile is constructed so that the energy of decomposition of at least one of the effective mass components is constrained in a radial direction. The ejection charge and/or the ignition decomposition charge, as well as at least one ignition delay device, is installed in the effective mass.

Abstract: A tubing conveyed perforating apparatus is shown which includes a tubular firing section which carries a plurality of explosive charges. The explosive charges are initially aligned with regions of reduced wall area provided in a tubular firing section which initially surrounds the charges. A piston sleeve is mounted on the exterior of the firing section. The piston sleeve has a plurality of apertures which are initially aligned with the regions of reduced wall area in the tubular firing section and thus with the explosive charges. Detonation of the charges causes the piston sleeve to shift so that the piston sleeve apertures are out of alignment with openings formed in the tubular firing section by the detonation of the charges, thereby trapping any resulting debris within the interior of the tubular firing section. Firing of the explosive charges opens upper and lower circulating ports so that sand or other debris can be reverse circulated up the interior of the well string to the well surface.

Abstract: A dual mode warhead is provided for use against both soft and hard targets nd capable of sensing which type of target has been struck comprising a casing made of a ductile material containing an explosive charge and a fuze assembly. The ductile warhead casing will mushroom and later split upon striking a hard target while still confining the explosive. Proper ductility and confinement are necessary for fuze sensing. The fuze assembly contains a pair of parallel firing trains, one initiated only by high and one by low impact deceleration. The firing train actuated by low impact deceleration contains a pyrotechnic delay to allow penetration of soft targets.

Abstract: The invention provides a new strip carrier assembly for carrying shaped charges, such as is particularly useful in perforating guns as are utilized to perforate oil and gas wells. The strip carrier includes a coupling member which couples adjacent strip carrier members together to form a contiguous assembly, and which further provides mounting system for a shaped charge so as to maintain uniform spacing even across the coupling junction. Additionally, the carrier assembly includes a novel tab assembly which cooperates with a charge carrier housing configuration to provide a single assemblage of parts which is capable of orienting shaped charges in any one of a plurality of desired orientations relative to the carrier strip.

Abstract: The present invention is directed to a connector for transmission tubes wherein a first initiated transmission tube transfers a signal to a second transmission tube within said connector.

Abstract: A coupling device (10) for coupling a detonator cap (20) with an unfixtured detonating cord (80, FIG. 3 ) after removing a shipping plug (41, FIG. 2 ), features a sleeve member (12) having a longitudinal sleeve bore (18) extending therethrough for receiving a detonator cap (20) therein. The detonator cap (20) extends to the transition end (22) of the sleeve member (12) so that the detonating cord (80) does not enter the sleeve bore (18). A nut member (14) has an aperture (24) for receiving the cord (80) and is secured to the sleeve member (12) with its aperture (24) aligned with the bore (18). A ferrule (16) is seated on the sleeve member (12) and grips the detonating cord (80) when the nut member (14) is secured onto the sleeve member (12).

Abstract: A formation is blasted with one or more arrays of elongated, chemical, explosive charges so as to produce relatively low levels of ground vibration. The orientation and velocity of propagation of explosion in each charge and the velocity of propagation of vibration in the formation are such that, at a selected outlying location, the onset of vibration from explosion of the first negligably small increment of the charge arrives a finite time before that from explosion of the last negligably small increment. The charges of each array are fired in accurately-timed sequence, with the times between initiations chosen so that, at the outlying location, the onset of vibration from explosion of the last small increment of each charge, except the last charge, arrives a negligably small increment of time before the onset of vibration from explosion of the first small increment of the succeeding charge.

Abstract: A through-tubing perforating gun includes an angularly shaped base strip having first and second surfaces and including a plurality of recesses in the first surface and a plurality of recesses in the second surface. A plurality of capsule charges are mounted in the plurality of recesses in the first and second surfaces of the base strip and are held in place within the recesses by a plurality of support rings connected to the base strip. The base strip is made of a material which will allow the base strip to withstand detonation of the capsule charges and will not shatter when the charges detonate; however, the support rings are made of a material which will allow the support rings to shatter when the capsule charges detonate.

Abstract: A blasting agent is disclosed for use in a borehole having a pressure resistant closure. The blasting agent is used in combination with a primary initiating system comprised of a detonator and an initiator for the detonator. The blasting agent is preferably a semi-fluid explosive material having a predetermined sensitivity. The sensitivity is related to the borehole diameter and the initiating system's strength, wherein the blasting agent upon initiation is transformed into explosive products by means of reaction front which consumes substantially all the blasting agent as the reaction front passes through the blasting agent. The reaction front has an average velocity of propagation of between 200 meters/second and 1,000 meters/second for at least 30% of the total length of blasting agent located in the borehole. Another aspect of the invention is a method of blasting wherein the average velocity of propagation of the explosive front in the blasting agent is in a range of between 200 m/sec and 1,000 m/sec.

Abstract: A perforating gun is designed to have explosive charges spirally disposed around its circumference in accordance with a displacement angle defined as (m/p)(360.degree.), where p is a whole number greater than 4 and m is a whole number greater than 1 but less than (p-1) and where m/p is an irreducible fraction. A U, or horseshoe, shaped retainer clip holds individual charges in respective holes and cavities of an outer carrier tube and an inner carrier tube to prevent horizontal or transverse movement of each charge and thereby hold it in contact with an axially extending detonator cord.

Abstract: A method of blasting cap-sensitive, non-nitroglycerine-sensitized explosives and an initiating assembly for use in the method are provided. The method comprises initiating a column of the explosives by directing two radial/forward shock forces from an initiator assembly substantially simultaneously along the column of the explosives towards each end of the column. The initiating assembly of the invention comprises at least two initiators assembled side-by-side so that their explosive ends are opposite. A moulded plastics holder (6) for holding two blasting caps (1, 8) in the required spatial relationship is also described.

Abstract: A method and apparatus for geophysical exploration wherein a seismic wave is passed through a bore hole so at to sequentially detonate a plurality of explosive charges disposed within said bore hole at spaced intervals. A preselected seismic wave magnitude represented by a stored voltage is compared with signals generated by electro-acoustic sensors associated with each charge. When the magnitude of a seismic wave in the bore hole equals the preselected magnitude, a voltage stored on a capacitor discharges into a detonator. Means are provided for varying the stored voltage representing the preselected magnitude from the surface of the bore hole and for detonating any unexploded charges which may after the initial seismic wave passes through the bore hole. A firing circuit is armed substantially simultaneously with the initiation of the seismic wave in the bore hole. The firing circuit is armed for only approximately 0.1 to 0.5 seconds thereby preventing late detonation which destroys seismic data.

Abstract: A method and apparatus for geophysical exploration wherein a seismic wave is passed through a bore hole so as to sequentially detonate a plurality of explosive charges disposed within said bore hole at spaced intervals. A preselected seismic wave magnitude represented by a stored voltage is compared with signals generated by electro-acoustic sensors associated with each charge. When the magnitude of a seismic wave in the bore hole equals the preselected magnitude, a voltage stored on a capacitor discharges into a detonator. Means are provided for varying the stored voltage representing the preselected magnitude from the surface of the bore hole.

Abstract: A perforating gun includes a base strip having an angular cross section, the base strip being a single unitary structure and essentially comprising at least two longitudinally disposed surfaces, a first surface and a second surface, a first plurality of capsule charges being connected to the first surface and a second plurality of capsule charges being connected to the second surface and interleaved with the first plurality of capsule charges, thereby phasing the capsule charges in the perforating gun. Since the gun utilizes capsule charges, good penetration into the formation is achieved. Due to the cross sectional configuration of the base strip, the phased capsule charges, when mounted on the strip, will easily fit within a tubing string previously used by non-phased capsule charge perforating guns.

Abstract: In the inventive shaped charge, the main charge and the propagating charge are held together solely by the barrier. This union is possible (and is distinguished by pronounced freedom from flaws) because the barrier is produced directly in the cavity in which it is to remain and is able to conform with the utmost accuracy to the surfaces of the charges. The barrier is advantageously formed under vacuum. Factors to be considered in the selection of the barrier material are its fluidifiability, its solidification and shrinkage behavior, and its compatibility with the explosive. Suitable barrier materials include single- or two-component foams, casting compounds, resins and adhesives.

Abstract: A well perforating gun and method of perforating a subterranean surface within a well bore are provided. The perforating gun comprises a tubular gun body having a plurality of external recesses formed therein and positioned in spaced relationship on a helical path around the peripheral surface thereof. The recesses are all equally spaced one below another relative to the longitudinal axis of the gun body with each successive recess being laterally spaced from a preceding one by an angle of about 150.degree.. Such spacing results in the first recess and every second one of the recesses thereafter lying on a second helical path and being laterally spaced by an angle of about 60.degree., and the first recess and every third one of the recesses thereafter lying on a third helical path and being laterally spaced by an angle of about 90.degree..