Threaded Fastener Selection 255

Allen wrench

A small, six-sided driving tool used for assembly that is compatible with a hex socket. Allen wrenches are also called hex keys.

alloy steel

A steel containing intentionally added materials that change the property of the metal. Alloy steels often have improved properties when compared to those of carbon steels.

aluminum

A nonferrous metal that is silvery white in color and lightweight. Aluminum fasteners resist corrosion and are good conductors of electrical energy.

American Society for Mechanical Engineers

ASME. An organization that publishes technical materials and sets industrial and manufacturing standards. The American Society of Mechanical Engineers provides standards for fasteners.

American Society for Testing and Materials

ASTM. The organization that develops standards for industry, government, and the environment to make products safer and more cost-effective. ASTM develops standards for fasteners.

bearing surface

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

beveled

Angled in comparison to the major surfaces of a part. Beveled bearing surfaces are a feature of flat head fasteners.

binding head

A type of thick fastener head with a deep slot and rounded sides. Binding heads are often used in electrical work.

black oxide

A coating used to add mild corrosion resistance to metals. Black oxide changes the appearance of metals and also increases their life spans.

brass

A nonferrous alloy containing copper and zinc. Brass has moderate strength and good corrosion resistance.

cadmium

A soft, bluish-white metal found in zinc ores. Cadmium is commonly used in metal alloys and as a coating on base metals.

cam out

The process of a driving tool slipping out of the driving recess. Camming out is common with Phillips drives.

carbon steel

A common metal that is an alloy of iron and carbon. The amount of carbon in carbon steel affects its strength, ductility, and malleability.

chamfer point

A type of fastener point with a beveled tip that guides the fastener into a hole. Chamfer points are very common and allow for easy assembly.

cheese head

A type of thick fastener head with a deep slot for increased driving power. Cheese head slots are often used in electrical work.

chrome

A hard gray metal often used as an alloying element in steel. Chromium is highly resistant to corrosion and wear.

coarse threads

Threads with larger pitches and thread depths. Coarse threads are easier to assemble and disassemble than fine threads.

cold working

Any metal shaping process that takes place when the metal is below its recrystallization temperature. Cold working adds certain properties to the metal, such as increased strength and improved surface finish.

cone point

A type of fastener point with a sharp, angled end. Cone points allow for deep penetration and are used for the permanent assembly of parts.

cone points

A type of fastener point with a sharp, angled end. Cone points allow for deep penetration and are used for the permanent assembly of parts.

conical washer

A type of washer with a raised, cone shape. Conical washers prevent loosening, without damaging parts, by flattening under pressure.

copper

A nonferrous metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper alloys, such as brass, are often used to make fasteners for the electronics industry.

corrosion resistant

The ability of a material to resist deterioration due to chemical or environmental exposure. Corrosion resistant coatings are added to steel and alloy steel fasteners.

countersunk

The cutting of a beveled edge at the end of a hole. Countersunk holes allow the head of a fastener to rest level with the workpiece surface.

driving recess

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

driving tool

A mechanical device that pushes one object into another object. Driving tools fit into matching driving recesses.

electrical conductivity

A material's ability to act as a medium for conveying electricity. Electrical conductivity depends on the material's structure.

environmental resistance

The ability of a fastener to resist forces in the environment that attempt to deform it. Environmental resistance can affect a fastener's performance.

fasteners

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

ferrous metals

A metal containing iron, generally as a primary ingredient. Ferrous metals are the most commonly used metal in the manufacturing of fasteners.

fillister head

A type of thick fastener head with a deep slot and a large, rounded top. Fillister heads provide better appearance.

fine threads

Threads with smaller pitches and thread depths. Fine threads have a greater stress area than coarse threads.

flat head

A type of fastener head with a blunt top and a beveled bearing surface. Flat heads are used with countersunk holes.

flat point

A type of fastener point with a flat or blunt end. Flat points are used in applications where the fastener might be frequently reset.

flat points

A type of fastener point with a flat or blunt end. Flat points are used in applications where the fastener might be frequently reset.

flat washer

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

Frearson

A type of driving recess with an X-shape. Frearson drives are less tapered than Phillips drives.

galvanizing

The process of adding a zinc coating to steel. Galvanized steel has superior corrosion resistance.

gimlet point

A type of fastener point with a sharp tip for penetrating a surface with the thread extending to the end of the point. Gimlet points are used on self-tapping fasteners.

grade

A classification that describes the quality of a material. The grade of material is important for avoiding fastener failure.

Grade 2

An inch series strength grade represented by no radial lines. Grade 2 is made from low-carbon steel.

Grade 5

An inch series strength grade represented by three radial lines. Grade 5 is made from medium-carbon steels that have been quenched and tempered.

Grade 8

An inch series strength grade represented by six radial lines. Grade 8 is made from alloy steels that have been quenched and tempered.

grip length

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

hardness

The measure of a material's ability to resist penetration, indentation, and scratching. In some metals, the level of hardness can be controlled through heat treating.

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.

head marks

A manufacturer-specific identification marking on fasteners for lot tracking. Head marks may be raised on the surface of depressed into the fastener head.

heat treating

The controlled heating and cooling process used to change the structure of a material and alter its physical and mechanical properties. Annealing, quenching, and tempering are heat treatments.

hex key

A small, six-sided driving tool used for assembly that is compatible with a hex socket. Hex keys are also called Allen wrenches.

hex socket

A driving recess with a six-pointed, hexagonal recess in the fastener head. Hex socket screw drives are one of the most common types of screw drive.

hexagonal head

A type of fastener head with six sides. Hexagonal heads are the most common bolt head.

hex-washer head

A type of fastener head with six sides and an included washer. Hex-washer heads prevent surface damage.

identification marking

Characters appearing on a fastener that often indicate the manufacturer and the standard specifications. Identification markings are helpful during fastener replacement.

Industrial Fasteners Institute

IFI. A nonprofit organization that represents the leading National American manufacturers of fasteners and publishes related standards. The Industrial Fastener Institute is responsible for publishing the frequently used IFI Book of Fastener Standards, which compiles the most commonly used standards into one volume..

International Organization for Standardization

ISO. An organization based in Switzerland that develops and publishes and maintains many types of standards. The International Organization for Standardization developed the metric thread standard and many metric fastener standards.

ISO metric thread standard

A system for cataloging and defining threads based on millimeters. The ISO metric thread standard was developed in Europe by the International Organization for Standardization (ISO), and is also known as the metric thread standard.

load

The force applied to an object by another object. Prolonged or heavy loads can cause deformation.

locking washers

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

lot

A group of similar parts created during the use of a particular tooling setup. Lots of fasteners are tracked by the manufacturer head marks.

low-carbon steel

A carbon steel that contains less than 0.30% carbon. Low-carbon steels are generally tough, ductile, and easily machined.

machine screws

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.

maintenance, repair, and overhaul

MRO. The range of activities that help keep products in operation. Maintenance, repair, and overhaul activities include planned or preventive service as well as rebuilding and alteration of products.

major diameter

The largest diameter of a thread. Major diameter is measured from crest to crest on an external thread and from root to root on an internal thread.

medium-carbon steel

A carbon steel that contains between 0.3% and 0.6% carbon. Medium-carbon steels are strong, hard, and not as easily machined as low-carbon steels.

megapascals

Mpa. A metric unit of pressure. A megapascal is equal to one million pascals (Pa).

metric thread system

A system for cataloging and defining threads based on millimeters. The metric thread standard was developed in Europe by the International Organization for Standardization (ISO), and is also known as the ISO metric thread standard.

Military standards

A United States system, often called mil-specs, used for standardization, quality, and security of products and equipment by the United States Department of Defense. Military standards are often used by industries needing high precision, such as the aerospace industry.

nonferrous metals

A metal that does not contain iron as the main element. Aluminum, copper, and zinc are nonferrous metals.

oval head

A type of fastener head with a round, elliptical shape and a tapered bearing surface for use in a countersunk hole. Oval heads improve joint appearance.

oval point

A type of fastener point with a rounded end. Oval points allow for adjustments without causing surface damage.

pan head

A type of fastener head that is very wide with a flat or slightly rounded top and rounded sides. Pan heads provide excellent clamping strength.

Phillips

A type of driving recess that has an X-shaped indentation designed to accept a Phillips screwdriver. Phillips drives are prone to camming out.

phosphate

An inorganic chemical salt of phosphoric acid. Phosphate improves the corrosion and wear resistance of a steel surface.

pilot point

A type of fastener point with a straight tip with a smaller diameter that extends past the thread to help guide the fastener into a hole. Pilot points make assembly easier.

pitch

The distance between corresponding points on consecutive threads. Pitch can be determined by measuring the distance between two adjacent crests or roots.

point

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

Pozidriv

A type of X-shaped driving recess with an additional cross recess that intersects the X-shape. Pozidriv drives allow for more torque.

proof load

A rating that specifies the stress that can be applied to a fastener and released without causing damage. Proof load is often used interchangeably with yield strength.

property classes

A designation system that categorizes the strength of metric fasteners. Property classes consist of numbers where increasing numbers represent increasing tensile strengths.

radial lines

A line on the surface of a nut that extends out like a circle radius. Radial lines denote SAE grades on fasteners.

Robertson

A type of driving recess that has a four-sided indentation designed to accept a special power-tool bit or screwdriver. Robertson drives are often used in construction.

round head

A type of fastener head that is dome shaped with a flat bearing surface. Round heads cannot be countersunk.

shank

The cylindrical length of a fastener that extends from the underside of the head to the point. The shank includes the threaded and unthreaded parts of the fastener.

shank diameter

The diameter of the part of the fastener extending from the underside of the head to the point. Shank diameter is approximately the same as major diameter.

slotted

A type of driving recess that has a single straight-line slot designed to accept a flat-blade screwdriver. Slotted drives are used in lower-torque applications.

slotted

A type of driving recess that has as a single straight-line slot designed to accept a flat-blade screwdriver. Slotted drives are used in lower-torque applications.

Society of Automotive Engineers

SAE. An organization that writes specifications and other data used in a broad range of industries. The Society of Automotive Engineers developed the AISI-SAE classification system along with the American Iron and Steel Institute.

stainless steel

Stainless steel exhibits moderate strength and ductility and a unique microstructure. Stainless steel fasteners are popular for their corrosion resistance.

standards

A policy and guideline established to ensure fastener compatibility, mechanical properties, performance, and other characteristics. Standards may designate the characteristics of fastener threads, or of the entire fastener.

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.

threaded fastener

A threaded device that holds objects together or grips material. Threaded fasteners include screws, nuts, and bolts.

torque

The applied force that attempts to twist or rotate a material. Torque is used to tighten threaded fasteners.

Torx

A type of driving recess with a six-pointed indentation to resist slippage. Torx technologies were developed by Camcar Textron, Inc. and are currently trademarked by Acument Global Technologies, Inc.

truss head

A type of fastener head similar to the pan head but with a round top. Truss heads are good for covering holes in metal.

Unified thread standard

A system for cataloging and defining threads based on inches. The Unified thread standard was developed by the United States, Canada, and the United Kingdom.

washers

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.

yield strength

A metal's ability to resist gradual progressive force without permanent deformation. Yield strength of fastener materials is usually expressed in pounds per square inch or megapascals.

zinc

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