I recently had a crossover pipe bolt seize onto the front manifold of my 88GT, and after failed attempts with a screw extractor I drilled through the bolt after cutting off the head. I just bought an 8mm tap and I'd like to know what size drill bit I should use before I run my tap through the hole. Anybody? Thanks in advance!

Depends on the size thread you are cutting - but here you go:

Tap size / Drill Size (mm)
8 x 1.25 / 6.8
8 x .5 / 7.5
8 x .75 / 7.25
8 x 1 / 7

Hope this helps

[This message has been edited by Jeff Smith (edited 04-08-2002).]

It's 8 X 1.25, thank you for the info!

In case you can't find metric drill bits:

6.8mm is roughly .2678", which comes out to be 34/127" (never going to find that bit!)

Either use a 1/4" (.25), or the next size up would be 17/64" (.265625)

I would go with the 17/64" if you can't find a metric bit.

quote Originally posted by FieroJoe: In case you can't find metric drill bits: 6.8mm is roughly .2678", which comes out to be 34/127" (never going to find that bit!) Either use a 1/4" (.25), or the next size up would be 17/64" (.265625) I would go with the 17/64" if you can't find a metric bit.

I went to Sears this afternoon and their 8mm X 1.25 tap recommended a 17/64" drill bit. Thanks! I might have the car running by the weekend.