2 replies to this topic

[nomininolife]

Hi Guys

This maybe a question but.......

What size drill bit do I need to use for converting the threads to 5/16?

Thanks

David

[Big_Adam]

my bolt bloke told me 0.5mm and the pitch of the thread - from the original size for the correct drill bit.

....but thats metric.....

[dklawson]

For "inch" size fasteners the rule-of-thumb is to take the major diameter of the fastener and subtract the pitch to determine the tap drill. In this case, 5/16" = 0.313" and the common pitch for this conversion is 24 threads/inch = 0.042"/thread. So, the tap drill would be 0.313-0.042 = 0.271" which is about 6.9mm. Go a little smaller on the tap drill for a higher degree of thread engagement.