How to Calculate Thread Length on a Bolt

At Arun Fasteners we are often asked about the thread length on differing size Hex Head Bolts.  Below is a helpful guide.

NOTE: It is measured from UNDER the head

Metric Bolt Thread Length

0 to 125mm
2 x Diameter + 6mm
125 to 200mm
2 x Diameter + 12mm
200+mm
2 x Diameter + 25mm

Imperial Bolt Thread Length

Thread length = 2 x diameter + 1/4" (up to 6"), 2 x diameter & 1/2" (over 6")

NOTE: It is measured from UNDER the head

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