I have a 23mm 1.5 tap for Toyota FJ-80 TRE's and I am not sure what size drill bit to use,I have looked at charts but I came up with different numbers 53/64 .8281 .905 7/8 13/16 Can somebody telll me the right bit and where I can get one ?


Scott

Here is a tip for selecting the proper size drill for any straight thread tap without a chart. Works everytime. If you don't believe it, do the math and compare to a chart.

Metric is easy. Subtract the pitch from the OD.
23 - 1.5 = 21.5mm drill
Convert to standard by dividing by 25.4
21.5/25.4= .846
27/32 = .843

Standard is a little tougher. Subtract the inverse of the pitch (1/pitch) from the OD.
For a 1/4-20 bolt it would be: 1/4 - 1/20 = .25 - .05 = .200
An F drill is .201"
It's always easier to tap if you pick a drill a couple thousandths bigger than what the numbers say is optimal.

3/8" - 16: 3/8- 1/16 = 6/16 - 1/18 = 5/16"

Also keep in mind most drills will actually drill larger than the drill itself, if you drop it right in. To get a truer hole it is best to pre drill a few sizes smaller then run your finish drill through.

Thanks !

Here is a tip for selecting the proper size drill for any straight thread tap without a chart. Works everytime. If you don't believe it, do the math and compare to a chart.

Metric is easy. Subtract the pitch from the OD.
23 - 1.5 = 21.5mm drill
Convert to standard by dividing by 25.4
21.5/25.4= .846
27/32 = .843

Standard is a little tougher. Subtract the inverse of the pitch (1/pitch) from the OD.
For a 1/4-20 bolt it would be: 1/4 - 1/20 = .25 - .05 = .200
An F drill is .201"
It's always easier to tap if you pick a drill a couple thousandths bigger than what the numbers say is optimal.

3/8" - 16: 3/8- 1/16 = 6/16 - 1/18 = 5/16"

:smokin: I'll have to remember that trick.

One of those little black "Pocket Ref" books is pretty handy for random knowledge, too.

:smokin: I'll have to remember that trick.

One of those little black "Pocket Ref" books is pretty handy for random knowledge, too.
I got a pocket ref not long ago. Great little book with more knowledge than anyone will ever need.

The key to remembering that formula is to remember the metric one. Metric thread pitches are in mm per thread (mm/thread), where standard are threads per inch (thread/inch). So it's the same formula for both, but you have to use the inverse on standard because of how they are called out. If you draw it out on paper it's some really simple geometry and trig.