# M13x.8 tap



## avbill (Jul 19, 2015)

if you take the different between the two measurements  you get 12.2 mm  for drill  for the tap. or 0.4805".  

What would thefts drill be for the tap?

12mm = .4724
12.2    = .4805
31/64 = .4824
12.5   =  .4921

Going smaller  seems a better idea  Am I correct on that assumption?

thanks


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## Brooks803 (Jul 19, 2015)

I use a 31/64


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## jj9ball (Jul 19, 2015)

I agree with the 31/64 that Brooks said.  I would add that the best way to know is to use 31/64 and if the threads are stiff or they bind a little then go just a little bigger.  12.3mm would also probably work.  Depending on the tolerances on your drill bits it really is about the same difference.   If all else fails you can use a small boring bar if you have a metal lathe.   The main thing is that you keep most of the .8mm thread.... say .6 or so.  If you get much smaller than that you may have a cap the slides on and falls off.


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## Joey-Nieves (Jul 28, 2015)

Maybe this will help I use a 75% thread Guhring, Inc. - Tap-Drill
I find that if the threads are to tight the pen "feels" wrong.
http://www.guhring.com/Tech/TapDrill/default.aspx


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## Brooks803 (Jul 31, 2015)

The flip side to which drill bit is also what dia to turn your tenon to cut your male threads.

I turn to 12.7 - 12.8 and use a 31/64 drill bit. Works great for me.


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