UNDERSTANDING FASTENERS

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.

Tensile strength- The maximum tensile-applied load a fastener can hold prior to facture (vertical stress)

Shear strength- The maximum load applied to a fastener’s axis that can be withstood prior to failure (horizontal stress)

Proof Load- 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.

FASTENER IDENTIFICATION

Color:

Grade 8 bolts tend to be yellow in color, which is zinc yellow dichromate plating.  Grade 5 bolts tend to be silver in color, which is clear zinc plating.  Stainless steel bolts have a dull grey finish.

Head Markings:

Imperial (Fractional) bolts are identified by the number of the lines on the head + 2.  A grade 5 bolt will have three lines on the head.  A grade 8 bolt will have six lines on the head.

Metric bolts will be designated by decimalled numbers. (8.8, 10.9, 12.9)

Country of Origin:

 Designated by manufacturer symbol on bolt head

THREAD PITCH

FRACTIONAL- THREADS PER INCH (TPI)

USS/UNC- COARSE THREAD

SAE/UNF- FINE THREAD

EX.  ¼-20 HAS 20TPI (USS / UNC)

        ¼-28 HAS 28TPI (SAE / UNF)

METRIC- MEASURED GAP BETWEEN EACH THREAD IN MM

EX. M10 X 1.5 HAS 1.5MM BETWEEN EACH THREAD

 

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