Glossary of Fastener Terminology

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Eccentric, Eccentricity: Two surfaces of a fastener are eccentric when thy do not have the same center or axis. The amount by which the centers or axes are displaced from each other is called eccentricity. This is not to be confused with Total Indicator Reading (TIR).

EFFECTIVE DIAMETER: This is the diameter of an imaginary cylinder coaxial with the thread, which has equal metal and space widths. It is often referred to as pitch diameter. Sometimes referred to as the simple effective diameter to differentiate from the virtual effective diameter.

EFFECTIVE NUT DIAMETER: Twice the effective nut radius.

EFFECTIVE NUT RADIUS: The radius from the centre of the nut to the point where the contact forces, generated when the nut is turned, can be considered to act.

Electro-Galvanizing: Electro-galvanizing is the process of coating metal with zinc by electroplating.
Elongation. Longitudinal stretching of a fastener caused by a tensile load due either to tightening or to the external load.

Electroless Nickel: A relatively thin, hard coating that can be applied to threads and deposited uniformly. Bright metallic in appearance this coating has excellent resistance to wear and corrosion.

Embedment: Localized plastic deformation which occurs in the vicinity of clamped fasteners or in the fastener threads.

Endurance Limit: The endurance limit is the maximum stress that a fastener can withstand without failure for a specified number of stress cycles. (Also called Fatigue Limit.)

Environmentally Assisted Cracking (EAC): A process that can occur with the use of high strength steel fasteners in which crack initiation and growth occurs in the fastener at a comparatively low stress level as a result of interactions that occur with the environment. Hydrogen is suspected of causing EAC in high strength steel fasteners, the hydrogen being produced as a result of chemical reactions (galvanic corrosion in a moist environment) or being present from a plating process that may have been applied to the fastener.

External Force or Load: Forces exerted on a fastener as a result of an applied loading to the joint.

Externally Relieved Body: An externally relieved body is a body on which the diameter of the entire body or portion thereof is reduced to less than the rolled thread blank size of the thread.

External Thread: A screw thread which is formed on an external cylinder, such as on bolts, screws, studs etc.

Extruding: Extruding is the process of reducing the size of some feature or diameter by forcing it through a die.

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