Glossary of Fastener Terminology

T

Taylor-Forge Method: 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.

Taper: Taper, as used for fasteners, is the angle between one side and the axis of the fastener. taper may refer to head, shank, or some other feature of a fastener.

Temper: Temper is the state of a metal or alloy involving its structure and mechanical properties. Temper varies from the annealed temper (soft) to spring temper.

Tensile Strength: Force or stress required to break a fastener when pulled in straight tension. When expressed as a force, lbs., it applies to a specific size part. Expressed as a stress, psi, means the force is applied over a specific area and it could apply to a range of sizes. For example, socket screws from No. 0 to 1/2 inch can withstand an applied stress of 180,000 psi.

Tension Fastener: A tension fastener is a fastener whose primary function is to resist forces which tend to elongate it.

Tension Washers: 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.

Thread: A thread is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder. This is known as a straight or parallel thread to distinguish it from a taper thread which is formed on a cone.

Complete Thread: The length of complete thread is the length of that cross section of a threaded length having full form at both crest and root. Where there is a chamfer at the start of the thread not exceeding two pitches in length, it is included within the length of the complete thread. The thread length on the drawing shall be the gaging length or the length of threads having full form. i.e., the partial threads shall be outside or beyond the length specified.

When designing threaded products, it is necessary to take cognizance of: (1) such permissible length of chamfer and (2) the first two threads which by virtue of Hl-L0 gaging practice may exceed the product limits and which may be included within the length of complete thread. However, where the application is such as to require a minimumor maximum number, or length, of complete threads the specification shall so state. Similar specification is required for definite length of engagement.

Effective Thread: the effective (or useful) thread includes the complete thread and that portion of the incomplete thread having fully formed roots but having crests not fully formed.

Incomplete Thread: this is also known as the vanish or washout thread. On straight threads, the incomplete thread is that portion at the end having roots not fully formed by the lead or chamfer on threading tools.

On taler threads, the crest at the end may also be not fully formed due to the intersection of the major cone of an external thread or the minor cone of an internal thread with the cylindrical surface of the work.

Left-Hand Thread: A thread is a left-hand thread if, when viewed axially, it winds in a counterclockwise and receding direction, All left-hand threads are designated LH.

Right-Hand Thread: A thread is a right-hand thread if, when viewed axially, it winds in a clockwise and receding direction. All threads are right-hand threads unless otherwise designated.

Total Thread: The total thread includes the complete or effective thread and the incomplete thread.
Threaded Fastener. A threaded fastener is a fastener a portion of which has some form of screw thread.

Thread Crest: 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.

Thread Flank: The thread flanks join the thread roots to the crest.

Thread Height: This is the distance between the minor and major diameters of the thread measured radially.

Thread Length: Length the portion of the fastener with threads.

Threadlocker: Can be a term used for a number of vibration resistant products but is now usually reserved for threadlocking 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.

Thread Root: The thread root is the bottom of the thread, on external threads the roots are usually rounded so that fatigue performance is improved.

Thread Runout: 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.

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.

Tolerance: a tolerance is the total permissible variation of a size: The tolerance is the difference between the limits of size.

Tolerance Class: 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.

Tolerance Grade: 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.

Torque Multiplier: A gearbox used to increase the torque produced by a small hand wrench.

Torque Wrench: A manual wrench which incorporates a gauge or other method to indicate the amount of torque transferred to the nut or bolt.

Torsion: Twisting force applied to a fastener during tightening.

Toughness: Toughness is the ability of a material to absorb considerable energy without fracturing.

Trimming: Trimming is the term applied to the process of shaping or sizing by forcing a part through a die of desired size and shape.

Tumbling: Tumbling is the process of cleaning or abrading parts in a rotating container, either with or without cleaning or abrasive materials.

Turn Of The Nut Method: See ANGLE CONTROLLED TIGHTENING

(Click on the letters below to browse the glossary terms)

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z