Glossary of Fastener Terminology

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Ream: To finish a drilled or punched hole very accurately with a rotating fluted tool of the required diameter.

Reamer: Tool used for enlarging holes previously formed by drilling or boring.

Recess Depth: The the distance measured parallel to the fastener axis from the intersection of the head surface with the maximum diameter of the recess to the bottom of the recess.

Recess Diameter. The recess diameter is the diameter measured in a plane perpendicular to the axis of the fastener over the intersection of the outermost extremities of the recess with the head surface.

Recess Eccentricity: Recess eccentricity is the amount that a recess in a recessed head is eccentric with the shank of the fastener.

Recess Width: The recess width is the distance measured in a plane perpendicular to the axis of the fastener across the intersection of the sides or wings of the recess with the head surface.

Recessed Head: A recessed head is a head having a specially formed indentation or recess centered in its top surface.

Reduced Diameter Body: A reduced diameter body is a body the diameter of which may range from the rolled thread blank size to the minimum major diameter of the thread and is common on screws having rolled threads. Sometimes referred to as undersize body,’ a term which is not recommended.

Reduced Shank Bolt: A bolt whose shank diameter is smaller than the nominal diameter of the bolt (normally the shank diameter of such a bolt is approximately equal to the effective diameter of the thread).

Reference Dimension: A reference dimension on a fastener is a dimension without tolerance used for information purposes only.

Relaxation: The loss of clamping force in a bolt which commonly occurs as a result of embedment. Can also be caused by gasket creep, differential temperature expansion or vibration loosening.

Relief: The amount one plane surface of a piece is set below or above another plane, usually for clearance or for economy in machining.

Rib: Ribs are small ridges of material usually formed longitudinally around the shank.

Righthand Thread: A screw thread that is screwed in by rotating clockwise. The majority of screw threads are right handed.

Rivet: A rivet is a headed metal fastener of malleable material used to join parts of structures and machines by inserting the shanks through the aligned hole in each piece and forming a head on the headless end by upsetting.

Rockwell Hardness Test: A measure of hardness by determining the depth of penetration of a penetrator into the specimen under certain fixed conditions of test. The penetrator may be either a steel ball or a diamond sphero-conical penetrator. The hardness number is related to the depth of the indentation and the higher the number the harder the material.

Rolled Thread: A thread formed by plastically deforming a blank rather than by cutting. The majority of standard fasteners have their threads formed by rolling. Most threads are rolled before any heat treatment operation. Significant improvements in fatigue life can be achieved by rolling the thread after heat treatment, this improvement is due to compressive stresses being induced in the roots of the thread. However, because of the increased hardness of the bolt blank, the die life can be significantly reduced. Rolling the thread also generally improves the surface finish which can have a beneficial effect on fatigue life.

Root Diameter: Identical to MINOR DIAMETER

Runout: Runout is a term frequently used interchangeably with eccentricity but which normally refers to the amount which the outside surface of one component of a fastener runs out with respect to the outside surface of another component. As such, it includes eccentricity, angularity and bow. The amount of runout is usually expressed in terms of Total Indicator Reading (TIR) or Full Indicator Reading (FIR). .

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