Abstract: There is provided a nut in which occurrence of galling is prevented. The nut in which a depth t of a counterbore hole is set to be greater than (D?d×cos ?)/tan ?, when a nominal diameter is D, an average value of a maximum outer diameter and a minimum outer diameter taking into account a tolerance of a bolt to be fitted is d [mm], an inner diameter of the counterbore hole provided on an insertion side of a screw hole is D+0.2 [mm], a pitch of a screw thread is P [mm], and ? satisfies ?=arc tan(P/d).

Abstract: A fastener including a bolt having an elongated shank having a first end, a second end opposite the first end, and a threaded portion having an external bolt thread, the bolt thread including a bolt pitch. The fastener includes a nut having a first end, a second end opposite the first end of the nut, and an internal nut thread extending between the first and second ends of the nut and adapted to engage threadedly the bolt thread of the bolt. The nut thread includes a nut pitch and a hardness that changes gradationally between the first and second ends of the nut. The bolt pitch of the bolt thread of the bolt is mismatched with the nut pitch of the nut thread of the nut.

Abstract: A method for manufacturing a bolting part, such as a screw or a nut. The bolting part having a head with a periphery having at least one shoulder extending in a radial plane. The method includes at least the following forming steps: shearing of a wire of material so as to obtain a part of determined length, calibration of the part so as to correct the geometry of the part, rough machining of the calibrated part so as to obtain the head of the bolting part, and finishing of the rough-machined part by means of a third punch so as to form a head having at least one shoulder. The calibration, rough machining and finishing steps being carried out only by cold heading.

Abstract: A method of creating a threaded fastener which includes a shank having a first, threaded portion and a hardened thread portion. The shank includes a thread extending outwardly from a shank body over a first length of the shank. A second portion of the shank includes a groove positioned coincident with the thread and including a turn ratio equal to a turn ratio of the thread. The shank comprises corrosive resistant stainless steel. A coil of hardened steel engages the groove to fill the groove along the second portion.

Abstract: The invention relates to a screw, having a shank which is provided with a thread, produced from a material which is suitable for a strength-increasing thermal treatment and is resistant to corrosion, and to the use of a screw of this type in a corrosive environment in conjunction with a corrosion-resistant component to be screwed, and, furthermore, to a method for producing a screw of this type. Screws of this type are used, in particular, for direct screwing.

Abstract: A method for integrally forming a drilling tip on a wire nail, in particular in order to produce a screw with the aid of a pair of pinching jaws, provides for the bulge formed by the displaced material during the integral forming of the drilling tip to be sheared off the drilling tip along the entire length of the cutting edges of the drilling tip produced and to be left connected to the drilling tip only along the longitudinal side edges of the latter by a predetermined breaking point.

Abstract: A manufacturing method and equipment for intensifying hardness of screws includes at least three steps. A first step is to have a steel wire forged into a first blank with a screw head and a screw shank. A second step is to convey the first blank into a thread shaping die to have the outer diameter of the shank of the first blank diminished to form a second blank through the first sectional cold forging region of the thread shaping die for intensifying the hardness of the shank. A third step is to have the second blank directly moved into the second sectional thread-forming region of the thread shaping die to shape threads and a pointed tail of the shank. Thus, both the second step and the third step can be carried out within the same thread shaping die, able to elevate shaping speeds and hardness of screws.

Abstract: The invention relates to a screw, particularly for attaching a superstructure to an intra-osseous implant. The extends along a longitudinal axis and comprises a head and a thread. The head comprises a bearing surface configured to cooperate with a bearing surface of the superstructure to hold the superstructure in position. The thread is configured to engage with a tapping to tighten the bearing surfaces of the superstructure and the screw. Between the bearing surface and the thread, the screw comprises a safety portion. The safety portion comprises a driving shape and a frangible section at the connection between the safety portion and the head of the screw, so that the driving shape remains attached to the thread if the frangible section breaks.

Abstract: A pedicle screw assembly and method of assembly are disclosed. The pedicle screw assembly includes a bone fastener having a head at a proximal end and a threaded portion extending between the proximal end and a distal end. The assembly also includes a compression member having a conical inner surface and a locking member having an outer surface adapted to mate with the conical inner surface of the compression member. The assembly may also have an elongated member and a set screw that has a threaded portion. The assembly may also have a receiving housing having a central bore extending from a threaded proximal end to a distal end and a U-shaped cavity positioned perpendicular to the central bore and configured to receive the elongated member.

Abstract: According to example configurations, a modified screw head includes one or more slots or grooved channels. A screwdriver device includes a tip that can be inserted into a cavity in the head of the screw to torque the modified screw into an object. The screwdriver device includes a sleeve. The sleeve slides along a shaft of the screwdriver. The sleeve includes inward protruding posts (e.g., pins, fingers, etc.). Sliding of the sleeve over the screw's head requires that inward protruding posts in the sleeve be aligned with the grooves on the sidewall of the screw's head. Subsequent to aligning and sliding the sleeve into the grooved channels of the screw's head, the user twists the sleeve to secure the screw head to the screwdriver's tip. The sleeve can be spring-loaded to pull the head of the screw toward a handle end of the screwdriver after a user releases the sleeve.

Abstract: A high strength screw (2), especially an ultra high strength screw (2) having a tensile strength Rm of at least 1400 N/mm2, having a bainite structure has a yield ratio of at least 0.95. The screw (2) belongs to the new strength classes 14.10, 15.10, 16.10 or 17.10. The high yield ratio is realized by heat treatment of the screw (2).

Abstract: A method for manufacturing a screw is disclosed where a blank is rolled between two rolling dies. In each rolling die a rolling profile has been formed that comprises a host of elongated depressions. The rolling die has a first and a second end which are spaced apart from each other in the direction of rolling. During rolling, the blank is moved relative to the die from the first end in the direction of the second end. The mean pitch of the centre lines of the depressions, which pitch is defined as the quotient of the changes in the positions of the centre line in the direction across or parallel to the direction of rolling, in a region of the first end of the rolling die differs from the mean pitch in a region of the second end of the rolling die.

Abstract: An insert for a tool for assembling a bone anchoring device including a bone anchoring element with a head and a shaft to be anchored in bone and a receiving part, the insert configured for insertion into a holder of the tool, the insert including an elongate body with a longitudinal axis, wherein a first recess configured to receive a shaft of a bone anchoring element extends on a surface of the elongate body along the longitudinal axis, has a first diameter, and is oriented towards a first radial direction relative to the longitudinal axis, wherein a second recess configured to receive a shaft of a bone anchoring element extends on a surface of the elongate body along the longitudinal axis, has a second diameter greater than the first diameter, and is oriented towards a second radial direction relative to the longitudinal axis different than the first radial direction.

Abstract: A bone screw is described which includes a one-piece threaded screw body composed at least partially of a rigid foam. The screw body is headless and includes a bore extending therethrough to define a cannula and thereby providing the screw body with an annular shape defining a radial wall thickness. At least a central portion of the screw body is formed of the rigid foam which defines a matrix having a plurality of inter-connected pores therein. The inter-connected pores are disposed throughout the complete radial wall thickness of the screw body from an outer surface of the screw body to an inner surface thereof within the cannula, such as to permit bone in-growth through the complete radial wall thickness of the annular screw body. The inter-connected pores and the cannula thereby respectively allow bone in-growth through the complete radial wall thickness and the full axial length of the screw body.

Abstract: A screw manufacturing method by thread whirling machining and others are provided which can solve problems due to thread rolling and cutting and which inhibits moving paths of inserts from interfering with a curved line of a desired screw upon going in and out, thereby providing the screw with a targeted curved line. In the method of manufacturing a screw, a mount angle of the screw is calculated by formulae below in case that a lead angle of the screw is different from the mount angle. mount angle=tan?1{n×pitch/(?×D1)}??(1) D1={(screw valley diameter+screw outer diameter)/2}+?T??(2) screw valley diameter?D1?screw outer diameter??(3) in case ?T>0, {(screw outer diameter?screw valley diameter)/2}×0.2<?T<{(screw outer diameter?screw valley diameter)/2}??(4) in case ?T<0, ?{(screw outer diameter?screw valley diameter)/2}<?T<?{(screw outer diameter?screw valley diameter)/2}×0.2??(5) where D1?0, ?T?0, and n indicates a number of threads.

Abstract: A fastener system is constructed wherein the installation and removal drive surfaces intersect an enlarged core diameter in a transitional surface that extends between the installation and removal surfaces of adjacent wings. The transitional surface has a concave form that conforms to the core diameter. The projections of the driver in the system are formed in a blunt shape.

Abstract: A screw anchor for insertion into concrete is disclosed. The screw anchor has an essentially cylindrical base body on whose outer lateral surface an external thread is provided and which has a receptacle arranged in the direction of the cylinder longitudinal axis originating from an axial end face. The receptacle has a load-bearing structure originating from the axial end face. A tool receptacle extending essentially in the direction of the cylinder longitudinal axis is provided in the receptacle, wherein the tool receptacle extends further into the receptacle than the load-bearing structure from the end face to the rotary drive of the screw anchor in the cylinder longitudinal direction.

Abstract: A polyaxial bone anchoring device includes an anchoring element having a shaft and a head, a receiving part having a seat for receiving the head, a pressure element to exert pressure onto the head, wherein the head is pivotable and can be locked at an angle relative to the receiving part, wherein an outer wall of the pressure element has a recess or a deformable portion, and an inner wall of the receiving part has a deformable portion or a recess, wherein the pressure element is movable from a first position wherein the deformable portion protrudes a first distance into the recess while the head is pivotable relative to the receiving part, to a second position wherein the deformable portion protrudes a second distance into the recess, such that a force holds the head at one of a plurality of releasable angular positions before locking the head.

Abstract: The present invention relates to dynamic bone fixation elements and a surgical method to stabilize bone or bone fragments. The dynamic bone fixation elements preferably include a bone engaging component and a load carrier engaging component. The bone engaging component preferably includes a plurality of threads for engaging a patient's bone and a lumen. The load carrier engaging component preferably includes a head portion for engaging a load carrier (e.g., bone plate) and a shaft portion. The shaft portion preferably at least partially extends into the lumen. Preferably at least a portion of an outer surface of the shaft portion is spaced away from at least a portion of an inner surface of the lumen via a gap so that the head portion can move with respect to the bone engaging component. The distal end of the shaft portion is preferably coupled to the lumen.

Abstract: Method for production of painted driving-in elements (8), the method comprising providing the elements (8) with heads (7) for driving the elements into a medium, providing a strip-shaped magazine (2) with holes (1) for ordered supply of the elements to a driving-in power tool, inserting the elements into the holes, and subsequently painting the heads of the elements while located in the holes.

Abstract: A fastening device includes a screw (1,21) with a thread part (2) and a shaft part (3,23), the shaft part (3,23) having a recess (4) at the free end for the insertion of a tool, and a sleeve (6,26) with an external thread (7) and an enlarged rim portion (8), which has means for the placement of a second tool. The screw (1,21) is formed by a rod-shaped screw blank made of hardenable steel, which has an enlarged head portion (5) at one end. The sleeve (6,26) can be mounted onto the screw blank from the other end and has a step, which can be placed on or against the head portion (5). The shaft part (3,23) is designed with a support section (16,22) for the pushed on sleeve (6,26) and the support section (16,22) can be generated by deforming the screw blank so as to hold the sleeve (6,26) on the shaft part (3,23) in such a manner that the screw (1,21) and/or the sleeve (6,26) can be rotated. The fastening device, is suitable for being screwed directly into massive materials, e.g.

Abstract: A headless wire binding screw for use in a circuit breaker contains a slotted drive in combination with a Robertson drive. The slotted drive is for use with a slotted-type driver (such as a slotted screwdriver) and the Robertson drive is for use with a Robertson-type driver (such as a Robertson screwdriver). The screw has a body with a diameter of constant size along the entire length of the body. The screw also has an external thread that is formed along the entire length of the body.

Abstract: A fastener system is constructed wherein the installation and removal drive surfaces intersect an enlarged core diameter in a transitional surface that extends between the installation and removal surfaces of adjacent wings. The transitional surface has a concave form that conforms to the core diameter. The projections of the driver in the system are formed in a blunt shape.

Abstract: A magnesium screw manufacturing method includes the steps of: providing a magnesium wire or rod; processing a directly-heating procedure, a thermal insulation material coating and directly-heating procedure or a directly-heating and thermal insulation material coating procedure on the magnesium wire or rod; forming a screw head and a screw thread of a screw blank from the magnesium wire or rod to produce a magnesium screw member.

Abstract: A method for manufacturing a bolting part, such as a screw or a nut. The bolting part having a head with a periphery having at least one shoulder extending in a radial plane. The method includes at least the following forming steps: shearing of a wire of material so as to obtain a part of determined length, calibration of the part so as to correct the geometry of the part, rough machining of the calibrated part so as to obtain the head of the bolting part, and finishing of the rough-machined part by means of a third punch so as to form a head having at least one shoulder. The calibration, rough machining and finishing steps being carried out only by cold heading.

Abstract: A wind turbine installation comprises anchor bolts having a sheath or sleeve which extends above the cement foundation and the overlying grout layer. If desired, the sleeve may partially extend inside the base flange of the wind turbine tower. The sleeve may be manufactured from polypropylene, polyethylene or other materials having satisfactory mechanical properties, primarily that the material be capable of withstanding sufficient plastic deformation to cause the material to conform to the shape of the threads of the anchor bolts without the material failing. This swaging operation results in a crimped end which forms an interference fit with the threads of the anchor bolt thereby preventing or limiting the intrusion of water or other liquids into the bolt-sleeve annulus during the installation of the turbine foundation.

Abstract: The invention provides devices and methods for stronger and more stable spinal and other orthopedic implant fixation through the use of an anchor for an orthopedic screw e.g, a pedicle screw. The anchor includes a relatively rigid proximal flange and a distal flexible portion that has an inner surface engageable by the screw shank as it is installed in a patient. For use, the distal portion of the anchor is located in a tract of the patient and the screw then installed through the anchor in the tract. During installation, outwardly-directed radial pressure of the screw shank upon inner surfaces of the flexible distal portion of the anchor can cause enhanced engagement of the bones or body structures by the anchor. The anchor flange can include teeth for engaging bones or other body structures, so as to provide improved support for the orthopedic installation.

Abstract: Disclosed is a method for manufacturing a screw with helical chip discharge channel, including providing a blank, subjecting an end of the blank to form a head and subjecting the blank to rolling to form one or more sections of threads. The screw is formed with one or more helical chip discharge channels, which can be of different helical angle according the different applications. The chip discharge channel can be formed by milling, rolling, or combined rolling and milling. The chip discharge channel is extended into the threads to form tapping edges. As such, the tapping operation is made effortless and the shape of the tapped thread excellent. The extending angle of the chip discharge channel can be changed according to different materials of the workpiece to be fastened. The length of the chip discharge channel can be selected according to different applications.

Abstract: A method comprising attaching a screw head to a bone fixator component, wherein the screw head comprises a first portion comprising a slot and an inwardly curved bottom portion; and a second portion comprising an outwardly protruding and expandable bulbous end extending from the inwardly curved bottom portion; and wherein the bone fixator component comprises a concave socket adapted to receive the screw head; securing the bone fixator component in a bone; securing a locking pin in the screw head; engaging the locking pin with the bone fixator component; inserting a longitudinal member in the screw head; and inserting a blocker in the screw head.

Abstract: The present invention provides a screw device which takes a heavy load in one direction along the axis of the screw shaft and only a light load in the opposite direction, the screw device capable of providing ease of control of preloading. The screw device of the present invention has a screw shaft 1 with an outer surface having a ball rolling groove 1a for rolling balls 7 and a roller rolling groove 1b for rolling rollers 6 both spirally formed thereon; a ball nut 4 with an inner surface having a ball rolling groove 4a spirally formed thereon facing the ball rolling groove 1a of the screw shaft 1; a roller nut 5 with an inner surface having a roller rolling groove 5a spirally formed thereon facing the roller rolling groove 1b of the screw shaft 1; a plurality of balls 7 arranged between the screw shaft 1 and the ball nut 4; and a plurality of rollers 6 arranged between the screw shaft 1 and the roller nut 5. The ball nut 4 and the roller nut 5 are connected along an axis of the screw shaft 1.

Abstract: A titanium alloy fastener made by: using titanium alloy to make a fastener body subject to a predetermined design, and then applying a heat treatment to harden the fastener body, and then processing the fastener body with a nitrogen treatment to form a titanium nitride coating on the whole surface of the fastener body.

Abstract: Screw (10), bolt or locking ring bolt (20), each exclusively produced by rolling as well as a method of production of such a screw (10), such a bolt or such a locking ring bolt (20).

Abstract: A self-drilling screw includes a head portion, a shank portion having an externally threaded section, and a drilling portion opposite to the head portion. The drilling portion has a main section and a tip section, two flutes extending helically through the main and tip sections, and two lands extending helically between the flutes. Each of the lands has a tapered face extending in the tip section and between the flutes, and a drilling edge formed on one end of the tapered face.

Abstract: The present invention pertains to a method of manufacturing a bi-metal screw comprising a sequence of procedures; wherein, the process preparation is for arranging a shank portion and a drilling portion made of different materials; the shank portion has a planar welding surface defined thereon; in particular, the drilling portion includes a conical section with a conical surface defined on the top face thereof. While operating, the conical section is gradually welded to the planar welding surface to form a composite screw, so as to smooth the air away for preventing the interspaces generated within the junction of the two portions and rendering the composite screw not to be slanted aside. Subsequently, an integral bi-metal screw is formed through the processes of precisely cutting and formation, thereby increasing the quality of the screw.

Abstract: A screw having in its head a recess that includes two or three non-circular superimposed recess-tiers. The depth of each recess-tier is less than 1.35 mm and there is less than 1° draw in each recess. The screw head recess is formed using a punch (10) in a cold heading process. The punch is formed in a profilating CNC machine, cutting the profiles of the punch to a tolerance of better than ±0.0025 mm.

Abstract: A screw (10) and driver (30) system comprises a range of screws and a driver. Each screw has a head (12) having a driving recess (14) in its surface (13) for engagement by the driver. Each screw has a longitudinal axis (100). The recess (14) of larger screws in the range have a plurality of superimposed recess-tiers (16a,b,c) of decreasing size with increasing depth from said surface. Each recess-tier has substantially parallel driving surfaces. They are substantially parallel the longitudinal axis. The driver and recess are shaped so that, when the driver is engaged with the recess of any screw in the range, torque applied to the driver is transmitted to the screw through said driving surfaces. At least one recess-tier (16c) of at least smaller screws in the range has a rib (20) which is parallel the longitudinal axis (100) and encroaches into the space of the recess-tier occupied by the driver when it is engaged with the recess.

Abstract: A threaded device such as a self-tapping screw or bolt, particularly for use in medical applications, provides a low-torque design that prevents a steady increase in the amount of torque necessary to drive the device into material as the device progresses. The design includes a thread that has a proximal section with a reduced diameter, thereby reducing the overall contact area between the thread and the material.

Abstract: The novel concept to be patented involves minutely indenting the standard fasteners along the pitch line at various points and utilizing the small material deformations around these indentations to provide substantial engagement to resist loosening of the joint under operational loads. The basic idea is to stamp a typical pattern (two are described below) on the fastener to achieve the advantages of a self-locking mechanism as well as enhance the torque and load carrying capability of the joint. Moreover, the indentations being in the order of few mils would not degrade the strength of the fastener, but would continue to provide sufficient load transfer across the joint without loss of preload. Furthermore, the joint can be disassembled and the fasteners can then be reused for the subsequent operations. These unique indentations on the fasteners can be of varying numbers, depths, geometry (spherical, elliptical etc.) and of various patterns (linear, staggered etc.

Abstract: A fastener is described having a head formed with a recess which accommodates a square head driver, symmetrical drivers, such as PHILLIPS™ style drivers, asymmetrical style cross head drivers, such as POZIDRIV® style drivers, and combination square and cross drivers without compromising performance of the drivers.

Abstract: In a process for the production of a screw comprising a low-alloy carbon steel, having a head, an adjoining holding portion and a functional tip which, in the outer region of limited radial depth, is of a greater hardness than the holding portion, in which the screw body is shaped by pressing and rolling and then the functional tip is subjected to a hardening operation, hardening is effected by momentary heating with a high level of energy transfer and subsequent quenching and is limited to portions of the periphery of the functional tip.

Abstract: A headed multi-lobed blank, method of manufacturing a self-tapping screw from the blank, and resulting multi-lobed self-tapping screw for joining thin workpieces provides desirable thread-forming characteristics at the conical tip and body portions, and improved resistance to vibrational loosening near the head. The resulting screw, obtained from the blank and method, incorporates a threaded tapered root portion between the screw head and body portion having a cross section that varies from nearly circular in the area adjacent to the underside of the head to a maximum out-of-round (or lobular) cross section at the intersection of the tapered root portion and the screw body.

Abstract: A cool-wrought pressing forming method for slotted headless screws includes five steps of using five different molds and five pressing heads for processing a unit of screw material cut from linear material for forming an unfinished screw with a slot in an upper end. A clamping member is provided for clamping a screw material for moving it from a first mold in a first step to a second mold in a second step after pressed by a first pressing head and then from a second step to a third mold in a third step, and so forth. The slot of a screw is formed by pressing to make the slot neat and without any hairy sides and look very flat, enhancing production effect and lowering cost.

Abstract: A method of making a UHMWPE body combined with a bolt, a cap screw, a reinforcing member uses a compression molding machine equipped with a male and female mold set. Particulate UHMWPE dispensed into the cavity of the female mold surrounds the head of the bolt and screw and reinforcing member. Pressure and heat applied to the particulate UHMWPE molecularly bonds the UHMWPE to the bolt, screw, and reinforcing member.

Abstract: The invention comprises a self-screwthread-forming screw of corrosion-resistant steel, which screw is partially precipitation-hardened. The invention also concerns a process for producing such a screw in which the screw is firstly shaped by pressing and rolling or by screwthread rolling or cutting or in other known fashion characterized in that the screw is then partially precipitation-hardened.

Abstract: A threaded fastener lighter in weight and easier to produce is made by the moderate temperature-forging, from a raw magnesium material that contains microcrystals whose diameter is about 100 &mgr;m or less. The raw material may be pure magnesium of industrial grade in one case, and alternatively be any magnesium alloy or such a composition as comprising as its matrix the alloy or pure magnesium, in the other cases. The raw material has a superplastic property and a fine-granulated metallographic internal texture, and when making the fastener, will be heated to 250-400° C. at which superplasticity takes place to facilitate the forging to form the fastener. A method proposed in the invention to make the fastener is thus such that the number of necessary processing steps is reduced and manufacture cost is lowered.

Abstract: A screw intended to be set in place and removed rapidly. The screw is characterized in that the threads are intended to take two positions: a first position wherein they project at the periphery of a body (1) and a second position wherein they are retracted into the thickness of the body (1). The screw further comprises a displacement member (27) intended to displace the threads from one position to the other and a device for locking the threads (29, 36, 27, 38) in the extended position.

Abstract: A fastener and method of manufacturing a threaded fastener with a tool-receiving recess in the fastener head are provided including a gauging indicator for indicating whether the recess is properly formed to meet standards. The gauging indicator is preferably in the form of a protrusion of a predetermined size on the fastener head which changes when the punch forming the recess becomes worn or broken. In this instance, the protrusion will be reduced in size as the material of the protrusion is displaced into the fastener head and other material of the fastener head is pushed into the areas of wear or breakage on the punch. Accordingly, the size of the gauging indicator provides an indication of whether the recess is meeting standards.

Abstract: A new machine for and method of manufacturing fluted pin fasteners and the pins produced thereby are disclosed which utilize a circular grinding arrangement of a plurality of grinders which grind flutes into a threaded pin. An internally threaded collar threads onto the pin. When the collar engages a surface of a work piece, resistance to further threading increases. When sufficient resistance to threading occurs, the driver deforms the lobes of the collar radially inward toward the axis of the collar. Material of the collar positioned internally from the lobes responds to deformation of the lobes and flows radially inward into the flutes of the pin to lock the collar, pin, and work piece together. The driver then rotates freely, and a joint has been made with a predetermined axial load thereby locking the component parts together.

Abstract: A new machine for and method of manufacturing fluted pin fasteners and the pins produced thereby are disclosed which utilize a circular grinding arrangement of a plurality of grinders which grind flutes into a threaded pin. An internally threaded collar threads onto the pin. When the collar engages a surface of a work piece, resistance to further threading increases. When sufficient resistance to threading occurs, the driver deforms the lobes of the collar radially inward toward the axis of the collar. Material of the collar positioned internally from the lobes responds to deformation of the lobes and flows radially inward into the flutes of the pin to lock the collar, pin, and work piece together. The driver then rotates freely, and a joint has been made with a predetermined axial load thereby locking the component parts together.

Abstract: A self-drilling screw is provided which is suitable for use with both relatively thick metal plates and relatively thin metal sheets. The screw is formed from a blank 1 which includes a shank 2 extending between a head 3 and drilling tip 4. The shank 2, adjacent the head 3, is formed with a frusto-conical enlargement 8. A thread 10, when formed in shank 2, is extended into enlargement 8 so as to create a final part 11 of the thread which, in use of the screw with sheet metal 12, distorts the sheet metal such that it firmly locks onto the enlargement 8. A shallow recess 6 is provided in the underside of head 3 surrounding the frusto-conical enlargement 8.