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eeler1
05-18-2009, 10:43 PM
I've got a 9/32-32 tap, need to drill a hole the right size. I'm thinking its between a 1/4 and 5/16, so that would be between about .235 and .260+/-? Maybe a K or L drill bit? Any suggestions for figuring a drill size for an oddball thread?

LES A W HARRIS
05-18-2009, 11:08 PM
9/32-32, about .2473"- .2548", letter "D" .246" will probably cut a tad large and be on the low, .250" dia in the midrange, "F" .257" a bit oversize!

Cheers,

hornluv
05-18-2009, 11:36 PM
Subtracting the pitch from the nominal major diameter will give you approximately 75% thread depth, so in this case pitch is .03125 and your major diameter is .28125, so you end up with .250 for the tap drill.

Paul Alciatore
05-19-2009, 02:32 AM
Subtracting the pitch from the nominal major diameter will give you approximately 75% thread depth, so in this case pitch is .03125 and your major diameter is .28125, so you end up with .250 for the tap drill.

SGW
05-19-2009, 07:52 AM

A quarter inch drill would probably be fine.

Lew Hartswick
05-19-2009, 08:24 AM
Yep. That "system" for metric tap drill works just fine for any
dimensioning system.
"Basic dimension minus pitch"
...lew...

eeler1
05-19-2009, 12:45 PM
Cool, and I already have a 1/4" drill bit to use. Thanks for the help guys.

lynnl
05-19-2009, 12:56 PM
Does that rule (nominal dia minus pitch) result in 75% for BOTH metric and std threads?

polepenhollow
05-19-2009, 04:25 PM
On a drill chart. find the proper size size tap drill dia for a 32 pitch thread. IE. (10-32- tap is a #21 (.157). <187- .157 = .020.