Abstract: A self-tapping, screw-type masonry anchor which can readily be turned into a hole drilled in a masonry structure to secure an object thereto, the installed anchor being highly resistant to pull-out forces. The anchor, which is fabricated of hard metal, includes a head engageable by a torque-producing tool to rotate the anchor, and a shank extending therefrom provided with a root section surrounded by a helical male cutting thread whose series of convolutions have sharp crests and extend from the leading to the trailing end of the root section. The crests of the male thread diameters are greater than that of the hole and decrease progressively from the leading to the trailing end to create a reverse taper. When the anchor is screwed into the drilled hole to tap its wall, the large diameter crest at the leading end of the male thread cuts an internal female thread in the wall having convolutions of substantially uniform diameter which intermesh with the reverse-taper convolutions of the male thread.

Abstract: An alignment and mounting apparatus for mounting two modules (10,12) includes a first portion having a cylindrical alignment pin (16) projecting normal to a module surface, a second portion having a three-stage alignment guide (18) including a shoehorn flange (34), a Y-slot (42) and a V-block (22) which sequentially guide the alignment pin (16) with successively finer precision and a third portion in the form of a spring-loaded captive fastener (20) for connecting the two modules after alignment is achieved.

Abstract: A fixing element for connecting materials of relatively low strength includes a unitary, one-piece plastic body. An external thread is formed on the plastic body for compressing and compacting the low strength material in the thread turns of the external thread. A first external thread portion has a taper at one end of the plastic body. A second portion has a taper at another end of the plastic body, while a third portion has no taper and extends between the first and second external portions. A penetration tip is connected to the smaller diameter end of the first external thread portion. Further, a stop collar is provided at the large diameter end of the second external thread portion. The penetration tip preferably is a self tapping screw made of a harder material than the plastic body. Further, the thread depth of the second external thread portion decreases along the second external portion as the second external portion approaches the larger diameter of the screw.

Abstract: A shape of the head part of the screw is improved and performance of insertion of the screw when punched and performance of fastening of the screw when seated as well as a finishing treatment upon completion of the fastening against a fastened member are improved. The head part is comprised of an upper large diameter part formed with a first seat surface of inverse truncated cone shape having an outer circumference of a curved concave surface and a small diameter part formed with a second seat surface of an inverse truncated cone shape concentrically and integrally connected to a lower part of the large diameter part and having its outer circumference of a curved concave surface, and an annular projecting edge is formed at a connection part between the seated surfaces of the two-stage curved concave surfaces.

Abstract: The present invention discloses a fastener for a trailer bed. The trailer bed is constructed of wooden planks placed on a metal frame. The screw has twin threads with a helix angle of substantially 10.degree. to a line perpendicular to the axis of the shank or the fastener, an included angle of substantially 60.degree., and a trilobular point which allows the screw to be drilled into wooden plank and swage threads in the wooden plank and metal frame. Torquing the threads forces the fastener into the metal frame and wooden planks and allows the screw head which is tapered to seat itself.

Abstract: A pin is disclosed that includes an elongated shaft having a constant diameter, and an elongated threaded portion having first and second axially separated ends, the first axial end being axially closer to the elongated shaft than the second axial end. The threaded portion has a root diameter that tapers linearly from a maximum value at the first axial end to a minimum value at the second axial end. The root diameter at the first axial end is substantially equal to the diameter of the elongated shaft itself. The pin also includes a drill end extending axially from the second axial end of the threaded portion such that the drill end is connected to the elongated shaft by the threaded portion.

Abstract: A thread-forming screw includes a tapered end portion formed by inserting a cylindrical blank between paired dies each having a straight portion and a tapered portion. The threads of each die are provided with undulations along their lengths corresponding to the circumference of the screw blank so as to form a trilobular thread on the screw which spirals around its circumference from one end of the screw to the other in a direction opposite to that of the threads. The cylindrical blank provides increased material at the tapered thread-forming location for forming fully crested threads, while increasing the length of the tapered portion of the die and screw provides greater stress relief for reducing the force required for thread formation and allows the screw to be driven into a workpiece more easily while maintaining a high strip force.

Abstract: Hole forming and selftapping screw of up to approximately 6 mm thread diameter for tapping into sheet metal of a thickness of up to approximately 1 mm comprising a head including a formation for receiving a tool, a thread shank and a cylinder member following thereon having a diameter less than the thread-pitch diameter of the thread shank, merging into a tapered hole forming member. The thread shank merges with the cylinder member via a taper extending over approximately four threads, a distance corresponding approximately to the four-fold sheet metal thickness. The hole forming member terminates in a convexly curved friction surface corresponding to a radius (R) of approximately 0,5 mm. The entire screw is formed in one piece of tempered steel having a tensile strength of up to approximately 1400 N/mm.sup.2, mechanically hardened steel respectively.

Abstract: A threaded fastener in the form of a bolt or screw for recutting damaged threads during installation in a previously threaded bore or for cutting threads in a non-threaded bore. The fastener comprises a threaded shank terminating in a headed end and in a non-threaded frustro-conical lead-in end. A cavity is formed in the shank extending longitudinally from the first shank thread adjacent the frustro-conical lead-in shank end toward the headed shank end. The cavity comprises a slot of obround peripheral configuration having a planar bottom and a depth greater than the depth of the shank threads. At the end of the slot, nearest the lead-in end of the fastener, a radial bore is provided in the shank having a depth up to the longitudinal axis of the fastener shaft and a diameter equal to the diameter of the curved end of the obround slot. The trailing longitudinal edge of the slot comprises a thread cutting edge.

Abstract: Disclosed is a bolt which comprises a short column portion formed at the extreme end of the thread portion thereof, wherein the short column portion has a diameter larger than the root diameter of the thread portion and smaller than the thread diameter thereof and the extreme end thereof is formed to a spherical portion and a method of manufacturing the bolt by which a thread portion and a spherical surface portion are simultaneously rolled. The bolt arranged as described above has an excellent guide property to a nut.

Abstract: A shape of the head part of the screw is improved and performance of insertion of the screw when punched and performance of fastening of the screw when seated as well as a finishing treatment upon completion of the fastening against a fastened member are improved.The head part is made such that the upper surface having an engaging groove to with which a screw driver tool is engaged has a spherical surface, and the head part is comprised of an upper large diameter part formed with a first seat surface of inverse truncated cone shape having an outer circumference of a curved concave surface and a small diameter part formed with a second seat surface of an inverse truncated cone shape concentrically and integrally connecteed to a lower part of the large diameter part and having its outer circumference of a curved concave surface, and an annular projecting edge is formed at a connection part between the seated surfaces of the two-stage curved concave surfaces.

Abstract: A fastener for securing fixtures to concrete or masonry. The fastener includes a dual-thread first stage for engaging a bore in the concrete and stabilizing and centering the fastener as it taps its way into the bore. A single-thread second stage has a pitch larger than the threads of the first stage for receiving particulate cut from the bore so that the particulate will not interfere with driving the fastener completely into the bore.

Abstract: A self-tapping screw-type masonry anchor which when turned into a hole drilled in a masonry structure to secure an object thereto is then highly resistant to pull-out forces. The anchor is fabricated of a metal whose hardness is such that when it rubs against a masonry surface it is abraded and worn thereby. The anchor includes a head engageable by a torque-producing tool to rotate the anchor, and a shank extending therefrom provided with a root section surrounded by a helical male cutting thread whose series of convolutions have sharp crests and extend from the leading to the trailing end of the root section. The crests have diameters greater than that of the hole which decrease progressively from the leading to the trailing end to create a reverse taper.

Abstract: A skull pin provides greater resistance to shear forces so that it may be more readily made of titanium, ceramic or gem stone, yet still prevents undue penetration, and can be tightened if wear or erosion of the skull results from cyclic loading. The pin is used with a halo or cervical traction ring, and has a main, externally threaded, circular cylindrical body, and a skull engaging portion. The skull engaging portions is formed by first and second concentric, in-line cylinders terminating in conical sections, the first conical section terminating in the second cylinder (which resists shear forces much better than conventional skull pins), and the second conical section terminating in a pointed tip. The first cylinder has a diameter of about 0.18 inches, the first conical section has a length of about 0.09 inches and approximately a 60.degree. taper angle, the second cylinder has a length of about 0.03 inches and a diameter of about 0.07 inches, and the second conical section has approximately a 60.degree.

Abstract: Toggle bolt having an anchor screw threaded over at least a portion of its length, on whose end which is to be anchored in the cavity a toggle is mounted for pivoting between the legs of a shackle, between an insertion position aligned with the anchor screw and a locking position in which it lies across the axis of the latter.

Abstract: A thread rolling screw has a continuous helical set of threads formed on a body. The threads have a tip section, an intermediate section, and a final section. In the tip and intermediate sections, the diameters of the crests progressively increase. In the intermediate section, relieved areas are spaced apart around the crests of the threads. In the final section, the threads are continuous and circular and of constant diameter. The crest of the last intermediate thread is the same diameter as the crests of the final thread section.

Abstract: A self-aligning bolt has an eccentric pilot tip extending forwardly of the externally threaded shank thereof. A self-aligning nut has an eccentric counter-bore formed therein on the side of the seating face and offset from the axis of the internally threaded bore of the nut.

Abstract: A stud for securing a cylinder liner to a head has a modified thread form engaging a threaded hole in the stud with an interference fit. The thread is rolled and all threads have the same pitch diameter except the endmost thread. Three relief channels are formed in the threads and extend axially from the stud end through several threads while some full threads remain to engage the hole. The relief channels decrease hoop stress in the threaded hole and allow debris developed during installation to escape from the thread interface to prevent entrapment therein.

Abstract: A blank and fastener formed from the blank for a thread-forming fastener which provides axially aligned driving. A tip portion of the blank is formed in a conical shape at an oblique angle to the shank portion of the blank. The blank formed as such is then formed with threads, however, the tip portion is formed with threads only about a portion of its outer surface. The resulting threaded fastener forms threads on an inside surface of a pilot hole in a workpiece in which it is inserted. The threaded fastener so formed minimizes driving effort and maintains proper alignment when the fastener is initially inserted and driven into an unthreaded pilot hole in a workpiece and also prevents cross-threading when the fastener is removed and reinserted into the workpiece.

Abstract: A threaded fastener or insert has a generally cylindrical body and about the body is formed a thread. Two sets of flutes are formed in the thread extending axially of the body. One of these sets extends deeper into the thread than the other set.

Abstract: A masonry screw anchor having two different constant diameter shank portions connected via a taper. Each portion has a set of constant diameter threads and intermediate smaller diameter protrusions with the threads and protrusions on the larger diameter shank portion being larger in diameter than the diameter of the threads and protrusions on the smaller diameter portion.

Abstract: An anchoring structure comprises an anchor rod which is secured to the inside of an anchor hole in concrete by a cementing material except for an upper section of the rod having a depth of at least 1.5 times the diameter of the anchor hole. The upper end of the anchor rod may be surrounded by an insulating sleeve which fits into the upper section of the anchor hole. The anchor rod may have a continuous groove formed therein, at least one surface of which has a slope of 15.degree.-50.degree.. The depth of the groove is at least as large as the maximum crack width expected to appear around the anchor in the concrete.

Abstract: This invention relates to an improvement of thread-forming fasteners comprising driving heads, shanks, work entering end portions without a thread and continuous rolled type threads on both the said shank and the said work entering end portions, the shanks being of arcuate triangular configuration in cross section which is characterized by three equally spaced lobes separated by relatively broad arcuate sides. The shanks are formed so that the radii of the lobes are gradually increased while the radii of the sides are gradually decreased toward the heads. And beside one of the threads in longitudinal section is of anti-symmetric triangular shape so that a slipping torque along the female thread formed thereby can be increased for easy entry in a workpiece in adding axial load during fastening operation and a slipping torque along the female thread can be decreased in axial loaded condition after it is seated on the workpiece.

Abstract: A thread-cutting screw where the edge of the screw is at least partially undulating. The undulating edge has recesses in the shape of a parabola interrupting the flank face of the thread. The recesses are asymmetrical so that the front flank face of the recess in the screw-in direction is steeper than the rear flank face in the screw-in direction, so that unscrewing the screw is more difficult than screwing-in the screw.

Abstract: Cervical traction tongs having cooperating first and second curved arms made of MRI and biologically compatible and CT transparent material. Skull pins having main bodies of MRI and biologically compatible and CT transparent material, and pointed skull engaging tips of radiolucent material (e.g. single crystal alumina ceramic) extend through openings at one end of the arms, while at the other ends the arms are connected together in an adjustable manner, so as to adjust the spacing between the pin pointed tips. The arms have enlarged circular end terminations having radially extending serrations which cooperate together, and are held in a position to which they are moved by a through extending bolt and nut. The arms have sufficient elasticity to provide constant pressure urging the pointed pin tips against the human skull during use. A flexible strand for applying tension is passed through an arcuate elongated opening in the serrated end terminations of the arms.

Abstract: A tapping screw having a shank having a head and a tapered tip portion. The shank is formed on its peripheral surface with threads. First and second drill edges are formed on the tapered portion and on the intermediate portion between the head and an tapered portion, respectively, so as to be independent of the threads. The first drill edge has a maximum diameter smaller than that of the threads in the rear thereof and the second one has a maximum diameter equal to or larger than that of the threads on the main portion of the shank.

Abstract: A locking screw having a head at one end, a special entry portion at the other end, and a trilobular shank portion extending from the entry portion toward the head. The screw is further characterized in that the thread profile is of a double angle configuration symmetrical about an axis perpendicular to the longitudinal axis of the screw. The entry section is tapered and is formed with a series of truncations which serve to clear progressively a contaminating coating in an internally threaded workpiece, such as a nut, when the screw is threaded therein.

Abstract: A self-tapping and threading bolt to replace bolts when the bolt holes have damaged or stripped threads. The self-tapping bolt has a self-tapping tapered end which is small enough to fit in the bolt hole into which it is inserted. It has two slots cut into the end which provides both channels for disposal of chips and to define the cutting edge of the self-tapping portion. The cutting edge of the self-tapping portion is decreased in radius behind the cutting edge to provide a relief so that the bolt can be turned with less torque into the damaged bolt hole.

Abstract: A screw or bolt has a conventional threaded shank and a tapered pilot or lead end for easy entry to a threaded receptacle or nut. A pilot lead extends axially from the end of the shank. In one form, the pilot is cylindrical having an axis that either intersects or is parallel to the axis of the shank. Partial threads extend around the portion of the periphery of the pilot and an unthreaded transition surface angularly spaced from, transversely opposite, the partial threads extends to the outer surface of the shank. In another form, the pilot is elliptical having partial threads extending over a portion of its periphery and an unthreaded surface transversely opposite the pilot threads.

Abstract: A locking screw having a head at one end, a special entry portion at the other end, and a trilobular shank portion extending from the entry portion toward the head. The screw is further characterized in that the thread profile is of a double angle configuration symmetrical about an axis perpendicular to the longitudinal axis of the screw. The entry section is tapered and is formed with a series of truncations which serve to clear progressively a contaminating coating in an internally threaded workpiece, such as a nut, when the screw is threaded therein.

Abstract: A fastening bolt set is disclosed which is used for attaching an object to a structure, and which comprises an ordinary bolt with a hexagonal or circular head, an internal washer having a long shape and having an annular projection, an external washer having an annular projection, and an ordinary nut for final tightening, all of the above components being connected by a string. This device is used where the back side of the structure is unreachable by hand or by means of a tool, and the working method is such that the bolt and the internal washer are sequentially inserted through the fastening hole, and the string connected to the bolt and the washer is pulled out of the fastening hole. Then the head of the bolt and the internal washer are combined together, the body of the bolt is passed through the fastening hole, and the head of the bolt and the internal washer are halted at the back side of the fastening hole.

Abstract: A threaded fastener has an eccentric tip with a smooth portion and a threaded portion. The smooth portion when viewed in side elevation defines an edge on a curve with an arcuate slope and the tip threaded portion is coincident with the shank to provide a threaded fastener which substantially eliminates axial and angular misalignment.

Abstract: A pin for fixing a panel to a support material is provided, having a shank (1) and a head (4), and a narrowed anchorage portion (5), a washer (2) for pressing the panel to be fixed against the support material and a guide (3) for limiting the penetration depth the shank (1). The pin, to be anchored within a material supporting the panel by means of a powder actuated tool does not damage the panel and ensures fixing of the pin with very good quality The guide (3) comprises a cylindrical tube which forms a hole within the panel, within which the cylindrical tube guide (3) is disposed so as to serve as a guide for the shank (1) of the pin as the same is being driven therethrough and into the support material.

Abstract: A threaded fastener for preventing cross threading comprises a head, a cylindrical threaded shank projecting from the head, and a tip section formed on the end of the shank opposite the head. The tip section has a generally circular cross-section and has at least one and preferably two partial threads formed on it. The tip section may be generally cylindrical, conical, frusto-conical or bullet shaped. A method of manufacturing an anti cross thread fastener comprises forming a fastener blank with a shank portion joined to a tip section having a tip threading side and a reduced radius side, and applying threads thereto.

Abstract: The present disclosure relates to self-piercing fasteners, such as studs, bolts or nuts, the method of attaching such fasteners to a panel and fastener installation apparatus, including the installation head and die button. The fastener includes a self-piercing and riveting annular wall which is driven into a panel supported against a die member by the installation head. The die member includes an annular die cavity surrounding a central projecting die portion which is telescopically receivable in the free open end of the fastener annular wall. The free end of the fastener annular wall includes a piercing surface which mates with a piercing surface at the outer edge of the projecting die portion to pierce a slug from the panel.

Abstract: Wood screw comprising a head for receiving a fastening tool and a shank extending from the head. The shank is provided at the tip thereof with a tip guide portion adapted to penetrate an article to be fastened while boring a hole into the article such as timber. The shank is provided at the head side thereof with a fastening screw portion having at least a single screw thread. A chips removing screw portion is disposed between the tip guide portion and the fastening screw portion. The chips removing screw portion has screw threads, the number of which is greater than that of the fastening screw portion. The screw thread lead angle of the chips removing screw portion is larger than that of the fastening screw portion.

Abstract: A specially designed holding device for holding a fuel pump push rod in place during the installation of a fuel pump on an internal combustion engine is threaded into an existing threaded bore which intersects the passage containing the push rod. The holding device comprises an elongated threaded member of relatively soft metallic material compared to that of the block, e.g. aluminum, and having safety means for preventing damage to the push rod comprising an undersized forward inner thread portion, i.e. the first 21/2 to 3 threads, which will strip more readily than the threads of the engine block in the bore when over tightened. Alternatively, the safety means comprises a relatively soft metallic inner end portion or tip on the holding device.

Abstract: A self-penetrating screw for penetrating sheet metal and then bolting a panel or other member to the penetrated sheet. The screw is hardened and has a penetrating point, a bolt-like shank and a head. The bolt-like shank is provided with machine screw threads and the tapered penetrating point has space threads with a pitch substantially greater, and preferably twice, the pitch of the machine screw thread.

Abstract: A self-tapping screw for use on concrete and masonry structures is disclosed. The screw has a helically threaded shank of uniform diameter. The crest diameter of the helical thread on the shank has a taper which increases gradually from the tip or entering end of the shank for a predetermined distance along the shank and then has a uniform diameter over the remaining portion of the helical thread. The helical threads have a spacing of 5-8 threads per inch for screw sizes in the range of 1/2 to 3/16 inch. Thread cutting notches are formed in the threads over at least the tapered portion thereof. The screw is hardened to a Rockwell "C" hardness of 48 or greater.

Abstract: A tapping screw having a tapered edge at a rear part of the tapered portion at its tip. The drill edge has the maximum diameter which is larger than the maximum thread diameter at the tapered portion and smaller than the maximum thread diameter at the shank. The drill edge allows the screw to be driven in more securely with a smaller driving force. The drill edge also has a greater lead angle than the lead angles of the threads on the tapered portion and on the shank rearwardly of the drill edge.

Abstract: A tapered screw member provided with a tapered external thread or a tapered internal thread, which comprises disposing a guide means somewhat higher than the crest of another tapered thread at a position connecting to the crest of the tapered external thread or the tapered internal thread, thereby engaging tapered threads smoothly, easily and quickly.

Abstract: A threaded element for forming a threaded profile in the wall of a bore formed in a material and for insertion into the bore so as to reinforce the bore. The threaded element includes a cylindrical stem having an external thread having a plurality of separate tapping lobes for cutting the threaded profile in the wall of the bore. The stem has an unthreaded radius smaller than the unthreaded radius of the bore and a threaded radius greater than the unthreaded radius of the bore. A recess is defined between each adjacent pair of tapping lobes. Each tapping lobe is defined by two cutting arcs formed at its opposite ends and a convex escape-gap arc is located intermediate the two cutting arcs. Each cutting arc has a convex configuration relative to the center of the stem, and the apex of each of the cutting arcs defines the maximum thread radius of the threaded profile, as measured from the center of the stem.

Abstract: A screw having a tapered and offset tip with a partial thread prevents cross-threading of the screw when inserted into a nut. The offset tip is a section of a conical frustum. The axis of the conical frustum section is offset from the axis of the shank of the screw. The conical frustum section is defined by those portions of a conical frustum contained within the outer radius of the screw shank. The partial thread is located on the side of the tip facing the direction of offset of the tip.

Abstract: A fastening element for packing sheets comprises a body having a lateral surface; a thread provided on the lateral surface; a head plate situated at an end of the body and having a diameter larger than a largest diameter of the thread; and a recess extending in the head plate and terminating in the body. The recess is situated centrally with respect to the head plate and has a part configured for receiving a tool for turning the fastening element.

Abstract: A self-aligning pivot bolt for mounting a belt tensioner idler pulley on a base member in which the bolt is formed with upper and lower cylindrical pilot sections separated by an intermediate threaded section. The base member has a bolt receiving opening formed with upper and lower inwardly tapered sections. The bolt and opening are dimensioned so that a lead thread of the threaded section engages an upper portion of the lower tapered section prior to the pilot sections engaging the respective tapered sections of the opening. After partial engagement of the threaded section the lower pilot section begins engagement with the lower tapered section to axially align the bolt within the hole followed by engagement of the upper pilot section with the upper tapered section. The softer metal of the base member flows into the root areas of the bolt threads to trap the bolt in the opening of the base member.

Abstract: A self-tapping, self-aligning thread repair insert is disclosed. The insert is an annular sleeve having a threaded interior surface, a partially threaded exterior surface, and an opening. The exterior surface has a tapered portion between a straight threaded portion and a straight thread-free portion. The thread-free portion and the opening are adjacent an end of the sleeve. The thread-free portion is free of threads for a distance of at least 1.5 thread widths from the end of the sleeve. The sleeve is made of a 400 series stainless steel. The sleeve is case hardened.

Abstract: A double end stud has a shank member including a central slide shank portion and threaded portions formed coaxially on both axial ends of the slide shank portion. The threaded portions are externally threaded in opposite directions. The double end stud also has a nut member carried by the slide shank portion of the shank member slidably in the axial direction but not rotatably with respect to the slide shank portion. In use, the nut portion is moved axially as the threaded portions are screwed into female thread portions of the two structural members to be connected, so that the depth of penetration of the double end stud into both structural members are optimized to ensure a high strength of connection between these structural members.

Abstract: An existing bolt on certain V-8 engines near and laterally inwardly of the engine fuel pump is aligned with the fuel pump push rod driven by the engine cam shaft. When installing a new fuel pump, the existing bolt is removed and a push rod holding screw of sufficient length to engage and hold the fuel pump push rod is temporarily installed in the threaded opening previously accommodating the removed bolt. The holding screw is turned manually until it engages the fuel pump push rod to hold the push rod elevated while the fuel pump is being installed. The procedure assures that the push rod will be in proper operative engagement with the fuel pump arm when the fuel pump installation is completed, following which the push rod holding screw is removed and the bolt is reinstalled in the threaded opening of the engine block. Haphazard and unreliable methods of holding the push rod up during the fuel pump installation with table knives, screwdrivers and a variety of crude tools are fully avoided.

Abstract: A bolt adapted for use in automated manufacturing line such as automotive vehicle assembly line, can be tightened from one side with a mechanical wrench (16). The bolt has a threaded portion (16) engageable with a nut (18), a pin-tail (18) gripped by the mechanical wrench, and a guide section between the threaded portion and the pin-tail. The guide section has a length (l) determined in relation to the thickness (L) of the nut. The length of the guide section is selected so that approximately the entire length of the pin-tail can protrude from the nut when the nut is preliminarily attached to the bolt with about one turn of rotation.

Abstract: The screw has a conventional threaded body, and a tapered leading end for easy entry to a tapped hole. A projection extends radially from the tapered end portion and when the longitudinal center lines of the screw and hole are misaligned, makes first contact with the threads on the tapped hole. As the screw is turned, the projection follows the tapped threads of the hole to bring the machine screw into alignment. When the projection tracks the internal hole threads, the positional relationship between the projection and the first screw thread brings the starting point of the first screw thread into contact with the starting point of the first thread at the entrance of the tapped hole.