Thread Strength Calculation

Present them and you will get comments. There are at least 3 persons very able to answer you question but surely you will get much more comments. It will be up to you to discern the good and the less good.

This should help you:

Bickford - "An Introduction to the Design and Behavior of Bolted Joints"

Sorry to not elaborate on it - I am going to bed.

I am getting only about 15% difference (of course I am calculating for tension rather than compression) and for that it is 114 (if I take for the BSW) then M40x 2 is 129mm

the 114 value I am taking at random (since the female tapped hole material and strength is not known)

for j=1 it is only 32.95mm vs 37.56 mm

But again materials being same, the same proportion should apply .

May we have a look at the calculations?

Are you sure that's a metric bolt, not some other thread? e.g. electrical. Nearest metric bolt is M39 with 4mm pitch, but this is a non-preferred size. Nearest preferred size is M42 with 4.5mm pitch. That's for metric coarse threads, the ones you get if you don't specify fine. Fine thread pitch is typically 0.6 - 0.7 x coarse.

1½" BSW has 6 TPI, so pitch is 4.23mm.

Cheers.........Codey