Overview of Threaded Fasteners 231

all-metal lock nut

A locking nut with deformed threads that add interference to resist loosening. All-metal lock nuts are also called distorted thread lock nuts.

assembly

The process of joining components together into a larger or completed part. Assembly methods include mechanical fastening, adhesive bonding, and welding.

bearing surface

The area of a component that contacts another object. The bearing surface on fasteners is the underside of the fastener head, or the nut, that makes contact with the part.

Belleville washer

A cone-shaped locking washer with a raised section that flattens to prevent loosening without damaging parts. Belleville washers are also called conical spring washers.

blind threaded hole

An internally threaded hole that does not go completely through a material or object. Blind threaded holes are typically used with screws.

bolt

A cylindrical threaded fastener with a head that usually mates with a nut. Bolts typically have blunt ends.

brass

A nonferrous alloy containing copper and zinc. Brass has high tensile strength and corrosion resistance.

carriage bolt

A bolt with a rounded circular head and a square neck. A carriage bolt's square neck prevents the bolt from turning while the nut is tightened.

castle nut

A locking nut with notches cut into the top that are assembled with cotter pins to lock the nut in place.Castle nuts are also called slotted hex nuts

chamfered

Angled or beveled along an edge. Chamfered surfaces allow parts to fit together, remove sharp corners, and protect against damage.

chips

An unwanted piece of metal that is removed from a workpiece. Chips are formed by thread-cutting screws.

conical spring washer

A cone-shaped locking washer with a raised section that flattens to prevent loosening without damaging parts. Conical spring washers are also called Belleville washers.

corrosion resistance

The ability of a material to resist deterioration due to chemical or environmental exposure. Corrosion resistance is one of the most important physical properties for fasteners.

cotter pin

A pin with two ends positioned parallel to each other before use. Cotter pins are inserted through holes and then bent back to lock the pin and other components in place.

cup point

A type of set screw point with an indented tip. Cup points are used for permanent and semi-permanent applications and offer good security.

disassembly

The process of taking apart a product, often with the intention of reassembly. Disassembly is made possible using mechanical fasteners.

distorted thread lock nut

A locking nut with deformed threads that add interference to resist loosening. Distorted thread lock nuts are also called all-metal lock nuts.

driving recess

The indentation on top of a fastener head. The driving recess is designed to accept a matching driving tool.

electrical conductivity

The ability of a material to act as a medium for conveying electricity. Electrical conductivity is aided by the use of tooth lock washers.

electroplated

A coating method that uses electricity and a conductive solution to deposit a layer of plating metal on a metallic or non-metallic workpiece. Electroplated zinc is a common coating on screws.

external threads

Threads formed on the outside of a cylinder. External threads can be found on bolts and screws.

fastener

A device that holds objects together or locates them in relation to one another. Fasteners can be threaded or non-threaded.

flat washer

A common washer that consists of a flat metal disc with a center hole. Flat washers are also called plain washers.

flats

The straight surfaces on the sides of a fastener's head. The flats allow a wrench to grip the head and tighten the fastener.

free-spinning lock nut

A locking nut that creates resistance only when the final torque is applied. Free-spinning lock nuts include special features to provide resistance, such as the locking washer on a Keps nut.

grip length

The length of the unthreaded section of a fastener's shank. Grip length is measured from the bearing surface to the first thread.

head

The end of a fastener that provides a surface for gripping and turning and allows it to bear loads. Head shape and style varies depending on the type of fastener.

hex bit

A hexagonal tool that fits into the head of a drill or screwdriver. Hex bits are used to fasten socket head cap screws.

hex bolt

A bolt with a six-sided head. Hex bolts are the most common type of bolt.

hex key

A hexagonal tool that is used to fasten socket head cap screws. A hex key is a type of wrench.

hexagonal

Having six sides. Hexagonal fasteners like nuts often accommodate a driving tool.

interference

An amount of overlap between two objects. Interference between threads can be used to prevent fasteners from loosening.

interference fit

A tight fit designed so that the smallest permissible shaft is larger than the largest permissible hole. Force is required to assemble parts with an interference fit.

internal threads

Threads formed on the inside of a cylinder or hole. Internal threads can be found in nuts.

jam nut

A thin locking nut that is assembled onto a bolt in addition to a regular nut. The jam nut provides extra resistance that helps prevent the joint from loosening.

Keps nut

A free-spinning lock nut with an attached locking washer. A Keps nut’s locking washer provides extra resistance when tightened to prevent loosening.

locking fasteners

A vibration-resistant fastener that protects against joint loosening. Locking fasteners can be threaded or non-threaded and often use multiple components to lock the fastener in place.

locking nut

A nut designed to prevent loosening of the joint when assembled onto a bolt. Locking nuts are used for joints that require extra security.

locking nuts

A nut designed to prevent loosening of the joint when assembled onto a bolt. Locking nuts are used for joints that require extra security.

locking washer

A washer designed to help prevent joint loosening. Locking washers are used for joints that require extra security.

locking washers

A washer designed to help prevent joint loosening. Locking washers are used for joints that require extra security.

machine screw

A screw with a blunt end that is assembled into a threaded hole. Machine screws are very common threaded fasteners that are similar to bolts.

machine table

The surface on which stock or work is held and located on many types of machines. Machine tables have t-slots that fit t-head bolts.

neck

A square section under the fastener head that prevents slipping and turning after assembly. Square necks are used by carriage and plow bolts.

non-threaded fasteners

A fastener that does not have threads. Common non-threaded fasteners include pins, retaining rings, and rivets.

nut

A fastener with a threaded hole that mates with a bolt. Nuts are often hexagon-shaped to accommodate a driving tool.

nylon insert lock nut

A locking nut with a nylon ring built into the top of the nut. Nylon insert lock nuts add interference to resist loosening.

pins

A thin, often straight, cylindrical non-threaded fastener used to secure the position of two or more machine parts. Pins are inserted through holes.

plain washer

A common washer that consists of a flat metal disc with a center hole. Plain washers are also called flat washers.

plow bolt

A bolt with a flat circular head and a square neck. A plow bolt's square neck prevents the bolt from turning while the nut is tightened.

point

The threaded end opposite the head of a fastener. Points may be flat or pointed.

proof load

A rating that specifies the load that can be applied to a nut and released without causing damage to the nut. Proof load is used to rate nut performance instead of tensile strength.

punch presses

A machine with a stationary base and an upper arm that moves along a vertical axis to shear, bend, or form sheet metal. Punch presses are often used to perform punching and stamping.

retaining rings

A flat, circular, non-threaded fastener with a hollow center and an open section. Retaining rings provide a shoulder and can be inserted onto a shaft or inside a hole with an internal groove.

rivets

A non-threaded fastener that consists of a shank and a head made of deformable material. Rivets are inserted through holes and the shank is formed into a head on the other side of the part.

screw

A cylindrical threaded fastener that either fits into a threaded hole or forms threads in a material. Screws may have blunt or pointed ends.

seated

Fixed in place. Seated free spinning lock nuts provided joint resistance.

self-tapping screws

A screw that forms or cuts threads in materials without pre-tapped holes. Self-tapping screws have pointed ends.

SEMs screw

A locking fastener consisting of a machine screw with an attached free-spinning washer. A SEMs screw typically has a locking washer but may have a plain washer.

set screw

A screw that is usually headless used to lock a component onto a shaft. Set screws come with a variety of points designed to fit into or create a matching recess.

shaft

A long cylindrical bar used to support rotating components or transmit motion. Shaft components are secured with set screws.

shank

The cylindrical length of the fastener that extends from the bearing surface to the point. The shank includes the threaded and unthreaded parts of the fastener.

slotted hex nut

A locking nut with notches cut into the top that are assembled with cotter pins to lock the nut in place. Slotted hex nuts are also called castle nuts.

socket

A hollow tool that fits over a nut or bolt completely. Sockets attach to various devices that are used to tighten or loosen fasteners.

socket head cap screw

A screw that is very similar to a bolt with a driving recess inside the head. Socket head cap screws require a hex key or a hex bit for assembly.

split lock washer

A locking washer with a split section that is intentionally bent out of shape. A split lock washer is forced back into a flat shape as the fastener tightens.

square-head bolt

A bolt with a four-sided head. Square-head bolts are often used in wooden assemblies.

stainless steel

A type of steel that contains more than 15% chromium. Stainless steel has corrosion resistance.

steel

A metal consisting of iron and carbon, usually with small amounts of other elements. Steel is the most common screw material.

structural bolt

A large, heavy-duty bolt used for structural applications in buildings and bridges. A structural bolt is a type of hex bolt.

stud

A cylindrical fastener that has external threads at both ends. A stud does not have a head.

tab lock washer

A locking washer with one or more flat extensions that are bent to lock the washer and nut in place. Tab lock washers may also have more than one hole.

tensile strength

A material's ability to resist forces that attempt to pull it apart or stretch it. Tensile strength specifies the load a fastener can withstand before it breaks.

tension

A pulling force that is directed away from an object and attempts to move, stretch, or elongate it. Tension is applied to fasteners when they are tightened.

T-head bolt

A bolt with a T-shaped head that matches the T-slots in a machine table. T-head bolts rotate to lock the bolt in place.

thread length

The length of the threaded section of a fastener's shank. Thread length is measured from the first thread to the point.

thread-cutting screw

A self-tapping screw that removes material in a hole to create threads. Thread-cutting screws produce chips.

threaded fasteners

A fastener that has threads to hold objects together or grip material. Threaded fasteners include screws, nuts, and bolts.

thread-forming screw

A self-tapping screw that displaces the material in a hole to form threads. Thread-forming screws do not produce chips.

thread-locking compound

A type of liquid adhesive applied to fastener threads to seal the joint and prevent joint loosening and corrosion. Thread-locking compounds are often used with studs.

threads

A raised helical ridge around the interior or exterior of a cylindrical object or hole. Threads help fasteners grip material and hold components together.

through holes

An internal hole that completely passes through an object or material. Through holes are often used with bolts and nuts.

tolerance

The unwanted but acceptable deviation from a desired dimension. Tolerance determines how much an object can vary from the desired dimension and still meet specifications.

tolerances

The unwanted but acceptable deviation from a desired dimension. Tolerance determines how much an object can vary from the desired dimension and still meet specifications.

tooth lock washer

A locking washer with teeth that grip into materials. Tooth lock washers may have internal teeth, external teeth, or both.

torque

A force that causes rotation. Torque is used to tighten threaded fasteners.

T-slots

T-shaped openings that run the length of a machine table. T-slots enable machinists to clamp vises and other workholding components onto the table.

twelve-point bolt

A bolt with a double hex, or twelve-pointed, head. Twelve-point bolts are common in the aerospace industry.

washer

A flat metal disc with a hole through the center. Washers are often used with threaded fasteners to spread the load and control joint tightness.

washer face

The completely flat side of a nut or the bearing surface of a screw head. A washer face is intended to contact the surface of a washer or a part.

wrench

A tool used for fastening nuts and bolts. Wrenches contain fixed or moving jaws or a shaped feature that grips nuts or bolts.

zinc

A bluish white metal that is corrosion resistant and has a relatively low melting point. Zinc is often used as a coating on screws.