Bolt Glossary

AASHTO  The American Association of State Highway and Transportation Officials oversees the advancement of transportation policies and standards for the industry.

anchor bolt  A steel rod or bar with one end intended to be embedded in concrete and the other end threaded and projected for anchoring material to concrete. The end cast in concrete may be straightbent hook, a forged head, or welded attachment to resist forces imposed on the anchor bolt.

annealing  Describes the process of heating and cooling steel to soften hardness caused by manufacturing or previous heat treating.

ASD  Allowable Stress Design (according to the AISC 9th Ed.)

ASTM  American Society for Testing and Materials, is a leading standards development organization. Portland Bolt participates as a voting member on ASTM Committee F16 on Fasteners. This committee has jurisdiction on over 60 fastener standards.

average coating thickness  This is determined as either the value obtained by analytical methods or the mean value of a specified number of local thickness measurements that are evenly distributed over the significant surface.

bar  This describes carbon and alloy steel bar that is produced from hot rolled or cast billets with the cross sectional dimensions that have a relatively constant dimension.

bearing-type connection  A bolted connection that assumes that shear forces are transmitted by the bolt bearing against the sides of the holes in the connected material. Often denote on drawings with an “X” (i.e. A325-X) which excludes threads from the shear plane or “N” (i.e. A325-N) which includes threads in the shear plane.

bend test  This test is meant to determine the toughness or ductility of a fastener. It is usually performed by bending the fastener through its axis or on a round mandrel.

bolt  A headed and externally threaded fastener designed to be assembled with a nut.

brinell hardness testing This is a common method of determining the hardness of metal products. A test is conducted by forcing a carbide ball indenter into the surface of the test specimen. The resulting indentation is measured and the brinell hardness number is calculated by using a formula that divides the test force by the indentation. Standards for this test are defined under ASTM E10.

cap screw  A fastener manufactured by cold forming, with tighter dimensional tolerances than a hot forged bolt.

carbon steel  A metal alloy that principle elements are carbon and iron. Contains other trace elements in undetectable amounts.

certification  A procedure and action to verify in writing a process or material meets a set of applicable standards. This helps ensure consist products for both manufacturer and end users.

clamp load  Also called initial load or preload, is created when tension is applied on a bolt and results in equal force and measures of the compression of two parts. It is commonly calculated as 75% of minimum proof load.

cold forming  Processing material by forcing metal through various dies, below the recrystallization temperature. Most mass produced fasteners use this technique and require large production runs with long lead times.

compression load  The load which tends to compress or shorten the member. The value for compressive strength may depend upon the degree of distortion.

corrosion resistance  This describes the ability of a fastener to resist corrosion under specified conditions. Hot dip galvanizing is a cost effective way to provide a high level of corrosion protection for a variety of applications and environmental conditions.

cut thread  A threading method produced by removing material from the surface with a form cutting tool.

destructive test  A test to determine the mechanical properties of a material or the behavior of an item which results in the destruction of the sample or item.

distributor  A person or organization who purchases fasteners for the purpose of reselling them. They will typically specialize in a certain industry and carry standard fasteners. A distributor may or may not alter the fasteners prior to resale.

ductility (externally threaded fasteners)  The measure of a fastener’s ability to deform prior to the point of fracturing. Machined test pieces are made to evaluate the metal’s elongation and reduction of area. The lower the ratio of its specified minimum yield strength to its specified minimum tensile strength, the greater the fastener’s ductility.

elongation  Measures the change in length based on a percentage of the original size.

extensometer  This device measures the linear deformation of a fastener to sense the elongation under tensile stress in a controlled test environment.

eye bolt  A bolt having one end which is a closed or open ring with a threaded shank.

fastener  A mechanical device that holds or joins two or more components in definite positions with respect to each other and is often described as a bolt, nut, rivet, screw, washer, or special formed part.

fastener identification marking  A stamp, paint, or other permanent identifier that may include manufacturer information and applicable grade markings for certification purposes.

fastener manufacturer  An organization that fabricates raw steel into a fastener meeting specified standards.

fastener quality  A fastener’s adherence to its specification for dimensional tolerances, mechanical properties, and other requirements stated under applicable standards.

fastener specification  A precise statement of set requirements to be satisfied by a fastener, its material, or its processing. It also indicates the procedure used to determine whether the requirements given are satisfied. This would include specifications like ASTM A194A449F1554 and SAE Grade 2.

fastener standard  A document which details the attributes of a finished fastener and includes such characteristics as geometry, material or chemistry, heat treatment, finish, testing lot size, and packaging. Examples would include organization like: Industrial Fastener Institute (IFI) and American National Standards Institute (ANSI).

fastener testing  A determination or verification that the fastener meets its specification requirements.

forging  The process of forming raw steel into specified shapes. Some examples of forged products would be hex boltsclevises, and barrier pins.

forging cracks  This may occur during fastener manufacturing at the cutting or forging operations and are located on the top of the head or on the raised periphery of indented head bolts.

galling  This can happen when a stainless steel fastener is tightened, the thin oxide layer on the surface of the steel may scrape off resulting in the nut and washer welding together. When disassembled, the welded material may be torn and pitted.

gimlet point  A term that describes a cone point that is threaded completely along the 45 to 50 degree point and is commonly found on lag screws.

grade identification symbols  Permanent markings denoting the specification used to manufacture a fastener. This would indicate the appropriate material, mechanical properties and other criteria used to produce the bolt.

heat analysis  A chemical analysis of a given heat by the producer, which determines the percentages of its elements.

heat resistance  This describes the extent to which a bolt retains specified properties as measured by exposure of the material to a certain temperature and environment for a specified time.

hex bolt  This refers to a bolt made to ANSI B18.2.1 and has different tolerances than hex cap screw.

high strength bolts  A term which is used commercially to denote ASTM A325 or A490 bolts which are primarily used in construction applications.

high temperature bolts  Bolts specifically manufactured from high temperature alloys to maintain tensile loads at temperatures between 500°F and 1800°F. Refer to ASTM A193 for more information.

hot-dip galvanizing  The process of the immersion of fasteners in a bath of molten zinc for a controlled time period to obtain specified coating weight or thickness. This is a cost effective method for creating highly corrosive resistant steel products.

hydrogen embrittlement  The process by which high strength steel becomes brittle and fractures following absorption of hydrogen. There is a danger of this occurring when attempting to zinc coat high strength bolts (e.g. ASTM A490ASTM A354 BD). This can occur during the acid washing process prior to galvanizing.

IFI  The Industrial Fasteners Institute is the trade association of the North American fastener manufacturing industry. It is a strong supporter of fastener standards and partners ASTM, ASME, SAE and other organizations to develops specifications. The Inch Fastener Standards (2003) is leading reference guide for mechanical fasteners technical data.

LRFD  Load and Resistance Factor Design (according to AISC 3rd Ed.)

machined specimen  This is a test specimen machined from a full-size fastener to specific dimensions to standardize test results; often specified when a full-size fastener cannot be reasonably or practically tested. This test is used to determine elongation and reduction of area.

material test report  A document verifying the raw material meets specified requirements and includes results of mechanical tests and chemical analyses.

mechanically galvanized  Describes a coating technique of applying cold zinc powder to bolts by either cold welding or barrel finishing.

mechanical properties  The fastener characteristics which relate to its reaction to applied loads; these properties may be those of the basic raw material or result from the manufacturing process.

nut  An internally threaded product intended for use on external or male screw threads such as a bolt or a stud for the purpose of tightening or assembling two or more components.

passivation  The process of forming an oxide film on the surface of stainless steel by chemical treatment to improve corrosion resistance of stainless steel fasteners. This process is usually done after the steel has been subjected to thermal treatment (i.e. hot forging).

pickle  The process of removing surface oxides by chemical means.

plain  Describes a fastener that is free of additional coatings or finishes like zinc, hot-dip galvanizing, or paint. Also referred to as “black.”

proof load (externally threaded fastener)  The tension applied load that a fastener must withstand without any indication of permanent deformation or failure. Proof load is typically calculated at 90-93% of the minimum yield strength.

proof load (internally threaded fastener)  The axially-applied load using a bolt or threaded mandrel that must be supported by a nut without indication of thread stripping or failure.

proof stress load  The proof stress is the amount of stress (on a stress -strain curve) where a material will exceed the elastic/plastic limit. In other words, it begins to get a permanent set on further stressing. The 0.2% is the offset from the normal stress/strain curve ( a line drawn parallel to the normal curve – offset 0.2% of strain).

quench  The process during heat treatment of submerging steel in a liquid medium to rapidly cool it, typically in water or oil.

quench cracks  Surface discontinuities in an irregular or erratic pattern on the surface of the fastener which may occur because of excessive thermal or transformation stresses during fastener heat treatment.

reduced diameter body  A fastener having a body diameter not less than the minimum pitch diameter of its thread nor more than its minimum full body diameter.

reduction of area  The difference between the original cross sectional area of a tensile test specimen and its minimum cross section after the test sample has fractured.

roll thread  The threading method that uses dies to displace rather than remove material in order to create threads. Often used in conjunction with reduced diameter body.

rotational capacity test “rocap”  A test in which a bolt is assembled in a steel joint or tension measuring device with a lubricated nut, and tightened to not less than 10% of the bolt proof load. After initial tightening, the nut is rotated through specified degrees of rotation, and torque values are obtained to assure proper performance.

SAE  Society of Automotive Engineers specification’s cover fasteners typically used in automotive, equipment, and machinery applications.

screw  A mechanical fastener designed to thread by turning the head into a tapped hole or to form its own threads during installation.

shear strength  A maximum load applied to a fastener’s axis that can be withstood prior to failure.

shear stress area  An area perpendicular to the fastener axis which is based on the root diameter (minor diameter) of an externally threaded bolt or screw.

slip-critical connection  The high-strength bolt clamps the connected parts in such a way that the shearing force is resisted by the friction between the parts, not by the shear on the body of the bolts. This is often denoted on drawings as “SC” (i.e. A325-SC).

stainless steel  A steel which has as its primary alloying element, chromium ranging from 10% to 30%. Other alloying elements such as nickel and molybdenum may also be added.

strain hardening  An increase in strength and hardness resulting from the cold working of steel. This is also referred to as work hardening.

stress relief annealing  A heating process applied to forged/headed fasteners to relieve any mechanical stresses generated during the forming process.

structural bolt  A heavy hex head bolt intended for use in structural applications. Most commonly graded as ASTM A325 or A490.

surface discontinuities  Irregularities of a fastener. These may include cracks, head bursts, shear bursts, seams, folds, thread laps, voids, tool marks, and nicks or gouges.

tap bolt  A bolt that is threaded to the under the head. ANSI compliant tap bolts are made to the same tolerances as hex cap screws.

tensile strength  The maximum tensile-applied load a fastener can hold prior to facture.

test report  A written or electronic document provided by the authorized party to certify that a tested fastener’s chemical and mechanical properties conform to the specification required.

thread galling  The displacement of material between mating threads during tightening, which causes contact points to shear, producing friction, increased resistance to tightening, and even seizing of the threads. Thread galling is most common with fasteners made of materials that self-generate an oxide surface film such as stainless steel.

tie rod  A piece of steel typically threaded on each end used in an assembly with clevises and turnbuckles, often used to support canopies, awnings and other building structures.

traceability  The capability to authenticate manufacturing history by documentation of raw material, heat number, locations, or application of the product.

ultimate tensile load  The maximum tensile-applied load a fastener can support prior to fracture, and normally expressed in terms of pounds per square inch (psi) or pounds-force (lbf).