Glossary S.T

SAE Specifications  

Standards developed by the Society of Automotive Engineers, Inc.  

SAE Standard Screw Threads  

The SAE Screw Thread Standard, as revised in 1954, conforms with the Unified and American Standard (ASA B1.1-1949).  

Secondary Operations  

Operations which include punching, shaving, trimming, drilling, sawing, milling, pointing, tapping and polishing, etc., are generally called secondary.  

Self-Locking  

Where binding action is self-induced on the body of the bolt, screw or nut to keep it rigid and prevent movement and vibration.  

Semi-Finished Hexagon Bolts  

Bolts with standard sizes ranging from 1/4" through 4" . Class 2A tolerance. The bearing surface is washer faced.  

Set Screw Points  

A screw with various type points, cup, cone, flat, oval, half dog, full dog, hanger or knurled, used to hold or "set" a collar on a shaft or hold pieces of this kind against movement. Screws are usually short, threaded entire length with the various type points for different applications against this movement.  

Screw Stock  

Metal in the form of wire or rod, ordinarily a free-machininig type of alloy, used for making screw machine products.  

Screw Thread  

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

Screw Thread Chasers  

Cutting tools having teeth spaced to match the pitch of the threads to be cut.  

Set Screw  

An externally threaded fastener with or without a head and having a formed point, designed to prevent relative movement of parts when screwed through one part upon or into another part.  

Shear  

To cut off sheet or bar metal between two blades.  

Shear Nut  

A fine threaded thin Castle or slotted nut.  

Sheradising  

This coating is intended for medium to long term protection; BS4921: 1988 specifies two coating thicknesses of 15mm and 30mm minimum. To accommodate these thicknesses on a bolt thread the nut thread must be overtapped. Precautions need to be taken to ensure that any loose coating material is removed from the nut thread before assembly.  

Shear Strength  

The stress required to produce fracture when impressed vertically upon the cross-section of a material. Expressed in psi.  

Shim  

A thin spacer of sheet metal used for adjusting.  

Shoulder Stud  

A stud similar to a collar stud but having the plain portion of a uniform diameter which is larger than the major diameter of the thread, used where the design requirements do not permit the separation of parts produced by a collar.  

Single Thread  

A single-start thread having lead equal to the pitch.  

Sleeve Nut  

A long nut with right or left threads for connecting two rods to make an adjustable member.  

Slip Washer  

A washer with an opening large enough to slip the washer over a bolt, and under the bold head. Also called a C washer.  

Slotted Head  

The head, of a bolt or screw, which has one or more slots across the top to fit a screw driver.  

Slotted Nut  

A hexagon nut having opposed slots at the end opposite to the bearing face which are perpendicular to the axis, designed for insertion of a cotter to secure the nut in place when used wiht a drilled fastener.  

Slotted Pin  

A pin that has a slot, either a square or round bottom, into which an external clip or key is affixed in a locking position.  

Socket Head  

A recessed head in which the sides of the recess are parallel to the body axis, into which a wrench fits. The recess is commonly hexagonal or fluted in form. Also designated as "internal wrenching head" .  

Spacers  

Pieces designed to prevent crushing of sandwich-type and other lightweight structural materials at fastening points. Sometimes called inserts.  

Spacers, Threaded.  Spacers with threads through which a bolt can be put. This saves weight by eliminating the nut and the reduction of the bolt length  

Spade Screws  

A threaded, round body with a finger tightening projection. (Regular Offset or Bent). Primarily used in places needed for frequent adjustments or for knock-down assemblies.  

Spanner Screws  

Special unslotted screws surface, in Round undrilled, Flat drilled and others, that require a special wrench.  

Spanner Wrenches  

Tools used to turn and tighten spanner screws.  

Spin  

To shape sheet metal by forcing it against a form as it revolves.  

Spline  

Raised portions of a shaft which fit into corresponding grooves in a pulley or some sliding member. They can either permit end movement or can be used as permanent fastening.  

Spline Nut  

A nut having external splines or ribs which hold it in place when forced into a hole of slightly smaller diameter.  

Spline Socket  

A recessed socket in the head of a bolt or screw to develop greater torque or driving ease without  "round" the recess.  

Split Rivet  

A small rivet having a split end for securing by spreading the ends.  

Spot-Face  

To finish a round spot on a rough surface, usually around a drilled hole, to give a good seat to a screw or bolthead, cut, usually 1/16 inch deep.  

Spring Lockwasher (also serrated - internal/external shakeproof)  

A hardened coil wire having a slightly trapezoidal section after forming which functions as a spring take-up device to compensate for developed looseness and the loss of tension between the parts of an assembly and to prevent the nut from turning.  

Square Neck Carriage Bolt  

A plain, truss or oval head bolt with a square neck to prevent rotation  

Square Nuts  

Nuts that are square rather than hexagonal.  

Stainless  

1. A trade name given to alloy steel that is corrosion and heat resistant. The chief alloying elements are chromium, nickel and silicon in various combinations with a possible small percentage of titanium, vanadium, etc. 

2. By AISI definition, a steel is called Stainless™ when it contains 4 per cent or more chromium.  

Stainless Steel  

Any steel containing four or more per cent chromium is classified as stainless.  

Step Bolt  

A plain, circular, oval head bolt with a square neck to prevent rotation  

Stress Relieve  

Heating to a suitable temperature, holding long enough to reduce residual stresses and then colling to minimize the development of new residual stresses.  Stripper Bolt  Discarded term for a shoulder screw.  

Structure Machine Screws  

A Flat Head Machine Screw (AN509C) with one included angle approximately 100 degrees. Usually made in slotted and recessed head types. With a "grip" or unthreaded body at the head.  

Studding  

A threaded rod. It may be threaded at both ends or continous.  

Swage  

To shape metal by hammering or pressure with the aid of a form or anvil called a "swage block" .   

Tap  

(v) To cut threads in a hole with a rotating tool called a "tap" , having threads on it and fluted to give cutting edges.  

Tap Bolt  

A fully threaded hexagon head bolt.  

Tap End Stud

A double-end stud having each end threaded for a different class of fit. The tap end has a Class 5 fit to produce an interference fit in a tapped hole for semi-permanent assembly. The nut end is threaded Class 2A for assembly with a standard nut.  

Taper of Head  

In flat bearing surface fasteners, the taper of a head or nut is the angle between a side and the axis.  

Tapped Hole  

A threaded hole in a part.  

Taper Pin  

A pin that tapers from the larger end to a smaller end at the rate of 1/4" per foot. The taper pin aids in hole alignment. 

 "Tee" Head Bolt  

Bolt whose head slightly curves in the shape of a "T" . Hence the name "TEE" Head Bolt.  

Tapping Screw  

A screw which is threaded to the head and designed to form or tap its mating thread in one or more of the parts to be assembled, of various types as follows:  

Tapping Screw, Type A  

A thread-forming type of tapping screw having a gimlet point and a thread of relatively coarse pitch and special form, used in punched, or nested holes in metal sheets or in treated plywood or special asbestos compositions 

Tapping Screw, Type B  

Also designate "type Z" . A thread-forming type of tapping screw, having a blunt point with tapered threads of moderate pitch, used with punched, drilled or nested holes.  

Tapping Screw, Type C  

A thread-forming type of tapping screw having a blunt point with tapered threads at the end, having UNC or UNF threads and designed for fastening metal sheets.  

Tapping Screw, Type D  

Also designated "type EC" . A thread-cutting type of tapping screw having the same thread as type C but provided with a fluted end produced at thread rolling or a milled slot (or slots) produced after thread rolling.  

Tapping Screw, Type F  

A thread-cutting type of tapping screw having the same thread form as type C but provided with a multiple flute tapered end to facilitate tapping.  

Tapping Screw, Type FZ  

A thread-cutting type of tapping screw having the same thread form as type B but provided with a multiple fluted tapered end to facilitate tapping.  

Tapping Screw, Type G  

Also designated "type EC" . A thread-cutting type of tapping screw having the same thread form as type C but provided with a slot across the end to facilitate tapping in hard materials or deep holes  

Tapping Screw, Type H  

Also designated "type DB" or "type 25" . A tapping screw having the same thread as a type B but provided with a slot in the end to facilitate tapping in plastics.  

Tempering  

Reheating a quench-hardened or normalized ferrous alloy to a temperature below the transformation range and then cooling at any rate desired.  

Terminal Stud  

A threadedd and collared pin having a plain cylindrical section, used as a contact terminal on electrical appliances. Some types are headed instead of collared  

Thickness of Thread  

The distance between the flanks of the thread measured at a specified position and parallel to the axis.  

Thread Milling  

A machining process whereby thread is formed on a surface by generating with a rotatiang toothed cutter. Each tooth takes an individual chip.  

Thread Rolling  

A cold-forging process whereby screw threads are formed by displacement of metal as opposed to cutting. The process is usually used for producing external threads and is seldom practical for small quantities.  

Thread Series  

Groups of diameter-pitch combinations distinguished from each other by the number of threads per inch applied to a specific diameter.  

Threaded Taper Pin  

Dimensioned the same as a standard plain taper pin with the addition of a threaded section usually at the small end. Used in equipment where removal may be required.  

Threads Per Inch  

The reciprocal of the lead in inches.  

Thumb Screw  

A screw with a flattened or roughened head to be turned with thumb and finger.  

Tinners' Rivet  

A small rivet having a head of the same form as a flat head rivet but larger in diameter, used in sheet metal work.  

Tolerance  

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

Tolerance Limit  

The variation, positive or negative, by which a size is permitted to depart from the design size.  

Tooth Lockwasher (also serrated internal/external)  

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.  

Total Thread  

Includes the complete or effective thread and the incomplete thread.  

Torque  

Torque is a force that tends to rotate or turn things. You generate a torque any time you apply a force using a spanner (wrench). 

Tightening the hexagon nuts on a machine screw or threaded stud is a good example. When you use a spanner (wrench), you apply a force to the handle. This force creates a torque on the nut. 

When the nut locks against a stop, that is, has tightened to its limit, the torque force is also applied to the screw or stud.  

English units of torque are pound-inches or pound-feet; the SI unit is the Newton-meter. Notice that the torque units contain a distance and a force. To calculate the torque, you just multiply the force by the distance from the center. 

In the case of the lug nuts, if the wrench is a foot long, and you put 200 pounds of force on it, you are generating 200 pound-feet of torque. If you use a 2-foot wrench, you only need to put 100 pounds of force on it to generate the same torque.   SI: Newton meter (Nm) 1 Nm = 0.737 lb-ft  English: Pound-inch (lb-in) 1 lb-in = 0.113 Nm Pound-foot (lb-ft) 1 lb-ft = 1.356 Nm  

Torsion (Torsional) 

 A rotational or twisting force. 

Of or pertaining to torsion; resulting from torsion, or the force with which a thread or wire returns to a state of rest after having been twisted round its axis; as, torsional force.  

Trim Heads  

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  

Truss Head  

Low rounded top surface with a flat bearing surface.  

Tubular Rivet  

A small rivet having a coaxial cylindrical hole in the headless end, designed for securing by splaying the end.  

Tumble  

To clean, smooth, or polish in a rotating barrel or drum by friction with each other, assisted by added mediums, as scraps, balls, sawdust, etc.  

Turn  

To machine on a lathe.  

Turnbuckle  

A coupling, threaded right and left or swiveled on one end, for adjustably connecting two rods.