T... Glossary of Fastener and Fixing Terminology
GLOSSARY ALPHA LOCATOR
A washer with a tab or tabs that can be bent or located to hold the washer in place. Product
TAMPER PROOF SCREW
A screw with a head designed to be driven by a unique driver. Also screws where the driver part of the head breaks off at a predetermined load. see tamper proof Product
An American term for a fully threaded hexagon head bolt, hexagon set screw. Product
A pin that tapers from the larger end to a smaller end . The taper pin aids in hole alignment. Product
Square and D shaped with various angles Product
Self tapping screw are generally fully threaded and designed to cut or form their own threads in steel plate on installation various types are shown below. POINTS
- Type A Self thread-forming tapping screw having a gimlet point and a thread of relatively coarse pitch, used in punched, or nested holes in metal sheets or in treated plywood; this is the most popular self tapping screw. Product
- Type B Also called " Z" . Self thread-forming tapping screw, having a blunt point with tapered threads of moderate pitch, used with punched, drilled or nested holes.
- Type C Self thread-forming tapping screw having a blunt point with tapered threads at the end, having UNC or UNF threads and designed for fastening metal sheets.
- Type D Also called " EC" Self thread-cutting tapping screw having the same thread as type C with a fluted end produced at thread rolling or a milled slots produced after thread rolling.
- Type F Self thread-cutting tapping screw having the same thread form as type C with a multiple flute tapered end to facilitate tapping.
- Type FZ Self thread-cutting tapping screw having the same thread form as type B with a multiple fluted tapered end to facilitate tapping.
- Type G Also called "EC" Self thread-cutting tapping screw having the same thread form as type C with a slot across the end to facilitate tapping in hard materials or deep holes
- Type H Also called " DB" or "25" . Self tapping screw having the same thread as a type B with a slot in the end to facilitate tapping in plastics.
A method developed by four engineers of the Taylor-Forge Company in Chicago in the 1930's that subsequently formed the basis of the ASME code for flanged joint design. The assumptions made by the method are now generally regarded as too simplistic. This method gives rise to the m and y gasket factors.
T HEAD BOLT
Forged Bolt whose head slightly curves in the shape of a "T" . Hence the name "TEE" Head Bolt. Product
TEE NUT PRONGED AND SOLID
Three and four pronged nuts used in the furniture industry, Solid Tee nuts fit into slots or the end of Tee bolts Product
TEE WELD NUT SLAB BASED
Thread round nuts fixed to a plate with or without welding pips. Product
Reheating a quench-hardened or normalized ferrous alloy to a temperature below the transformation range and then cooling at any rate desired.
The maximum load per unit of original cross-sectional area obtained before rupture of a tensile specimen.
A general name given to spring washers, curved washers, Belleville washers and disc springs. This type of washer provides a relatively low stiffness (compared to the joint stiffness) and can be used to act as a spring take-up with a bolt to prevent movement between parts.
A threaded and collared pin having a plain cylindrical section, used as a contact terminal on electrical appliances. Some types are headed instead of collared.
The top part of the thread. For external threads, the crest is the region of the thread which is on it's outer surface, for internal threads it is the region which forms the inner diameter.
The thread flanks join the thread roots to the crest.
THREAD FORMING SCREWS
This is the distance between the minor and major diameters of the thread measured radially.
Wire threaded insert is typically used for tapped hole repair or to improve the thread stripping strength of softer metals such as zinc and aluminium. The inserts are assembled into a previously tapped hole using a special driving tool. Thread locking compounds are frequently used to secure the insert if the assembly is subject to vibration. Product
Inserts that tap a thread metal thread into plastic parts. Product
Length the portion of the fastener with threads.
Can be a term used for a number of vibration resistant products but is now usually reserved for thread-locking adhesives. Specifically, a liquid anaerobic adhesive applied to nut or bolt thread, once hardened it fills the inner spaces between the threads to produce a solid plastic of a known shear strength. Product
The thread root is the bottom of the thread, on external threads the roots are usually rounded so that fatigue performance is improved.
The portion at the end of a threaded shank which is not cut or rolled to full depth, but which provides a transition between full depth threads and the fastener shank or head.
A screw with a flattened or roughened head to be turned with thumb and finger. Product
Designed to be screwed into concrete with a special spaced thread to grip the concrete walls. Product
TIN/ZINC ALLOY ELECTROPLATING
Tin/zinc alloy coatings (typically 70% tin and 30% zinc) are applied to threaded fasteners to provide a corrosion resistant coating. One of the advantages of such coatings is that bimetallic corrosion will not occur when placed into contact with such metals as aluminium or steel.
Tips at the end of the set screw are in various materials and are designed to reduce damage. Product
A combination of tolerance grade and a fundamental deviation which is given to an internal or external thread. A tolerance class for an internal thread when combined with the tolerance class for an external thread gives the class of fit for the mating threads.
The difference between maximum and minimum metal conditions for a tolerance applied to a screw thread. For metric threads the tolerance grade is given a number.
TOOL POST SCREW
Square headed Tool post screws have a reduced square head and were originally designed to hold cutting tools onto tool posts; they have generally been replaced by the socket head screw. Product
TOOTH LOCK WASHER
A washer, usually a thin disk with prongs or projections, which is elastically deformed when assembled with a threaded fastener, so that the prongs, on which the pressure is localized, resist loosening of the fastener. Fan Disc Shakeproof
A type of prevailing torque all metal lock nuts similar the Stover ® nut Product
A rotational moment; it is a measure of how much twisting is applied to a fastener. The units used to measure torque are in the form of force times length. Usually measured in newton-metres (Nm) if metric units are used or pounds feet (lb-ft) when imperial units are used.
A gearbox used to increase the torque produced by a small hand wrench.
A manual wrench which incorporates a gauge or other method to indicate the amount of torque transferred to the nut or bolt.
TORX HEAD ®
Torx developed in 1967 by Camcar Textron, is a screw head with a 6-point star-shaped pattern. A popular generic name for the drive is star, the official generic name, hexalobular internal drive. This is abbriviated as 6lobe.Torx screws are commonly found on automobiles, motorcycles, hard disk drives, computer systems and consumer electronics. Initially, they were sometimes used in applications requiring tamper resistance or resistance to caming out. Product
TREP ® WASHERS
The TREP® spring washer is made up of three or four smooth, inseparably assembled tapered spring washers that maintain a high level of tension in the screw while conserving considerable elastic energy stored in a small volume. This washer guarantees that the assembly will not loosen in the event of crushing, material expansion, wear or vibration. It compensates for expansion gaps and its elasticity maintains optimal tension in the screws and bolted assembly. Product
Similar to the 82 degree flat and oval head machine screws except that the size of head for a given size screw is one or two sizes smaller than the regular flat and oval sizes
A Trivalent chromium passivation Cr3 that has replaced the toxic Hexavalent chromium on fastener coatings.
Low rounded top surface with a flat bearing surface similar to a mushroom head.
A small rivet having a coaxial cylindrical hole in the headless end, designed for securing by splaying the end. Product
A coupling, threaded right and left or swivelled on one end, for adjustably connecting two rods. Product
TURN OF THE NUT METHOD
A tightening procedure in which a fastener is first tightened by a pre-selected torque (called the snug torque) so that the clamped surfaces are pulled together, and then is further tightened by giving the nut an additional measured rotation. Frequently bolts are tightened beyond their yield point by this method in order to ensure that a precise preload is achieved. Bolts of short length can be elongated too much by this method and the bolt material must be sufficiently ductile to cater for the plastic deformation involved. Because of the bolt being tightened beyond yield, its re-use is limited.