How to Calculate a Bolt Thread Length

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

Bolt Thread Length

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

We’ve listed below a range of bolt sizes as an example:

Bolt Size Thread Length
M8 x 70
22mm
M10 x 180
24mm
M12 x 200
49mm
M14 x 280
53mm
M16 x 190
44mm
M18 x 300
61mm
M20 x 140
65mm
M22 x 360
69mm
M24 x 100
54mm

Here are some examples of some Bolts we stock-

NOTE: It is measured from UNDER the head

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