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 Post subject: Drill bit size for 5/8-24 tap
PostPosted: Thu Jun 19, 2008 12:05 pm 
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Silent But Deadly

Joined: Thu Nov 16, 2006 11:17 pm
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What size drill bit do I need for 5/8-24 tap? I need to make a fitting and thread it.


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PostPosted: Thu Jun 19, 2008 12:16 pm 
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Silent But Deadly
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Joined: Mon Aug 06, 2007 2:22 pm
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Location: J-Vegas, NC
19/32 for a 50% thread and 37/64 for a 75% thread.

http://www3.telus.net/public/aschoepp/tapdrill.html


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PostPosted: Thu Jun 19, 2008 1:20 pm 
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I would do 9/16. This will give a little more than 75% threads.

75% threads are for bolts and stuff, and made for high-speed tapping.


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PostPosted: Fri Jun 20, 2008 11:45 pm 
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Silent But Deadly

Joined: Thu May 17, 2007 10:40 pm
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A little trick for those that need a tap-drill size.

Lets say you have a 1/4-20 bolt.

You need to tap a hole for it to fit in, but don't know the tap drill size.

No problem.

Take the pitch of the thread( in this case 20) and divide the pitch by one.

1 divided by 20 is .050 or 50 thousandths.

Take the diameter of the thread( in this case .250) and subtract the .050 for a total of .200.

That is your tap drill size.

It works well and is always within a few thousandths of the standard tap drill charts. The standard tap -drill size for a 1/4 -20 thread is a number 7 drill bit..which is .201 diameter.

Lets do another.
a commonly used size 3/8 -16.

1 dived by 16 is .0625.
.375 -.0625= equals .3125 or 5/16 drill bit. Guess what? The tap drill size for a 3/8-16 is a 5/16 drill bit.

Amazing isn't it?


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PostPosted: Sat Jun 21, 2008 6:29 am 
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Dunce
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rsilvers wrote:
I would do 9/16. This will give a little more than 75% threads.

75% threads are for bolts and stuff, and made for high-speed tapping.


I just ran some with the 37/64 drill, and I got a full or very nearly full thread form. If it's not complete, it's within .005" on the diameter of complete. I'm looking at a flat on the top of the thread of about .006" and I would guess it's probably what? .004" at 100% thread?

This is with my eye, but I can't have more than .010" flat on the ID thread, and it looks a lot closer to .005"

It threaded to my Tornado threaded bolt gun nice and snug.

I was using a split point titanium coated HSS bit. American made. The import s--t probably cuts .005-.010" oversize, something to look out for.

You know what actually, I know the reason why- the chart is calling out 5/8-18 threads. The 5/8-24 thread is a finer thread, IE larger hole size, so the 75% drill for a 18 pitch is more like a 85-95% drill for a 24 pitch I believe.

It took me a while to remember. It's been a while since I bought the bit.


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PostPosted: Sat Jun 21, 2008 6:48 am 
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Silent But Deadly
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Joined: Mon Dec 18, 2006 5:55 pm
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Location: Northeast Georgia...near UGA
HotGuns wrote:
A little trick for those that need a tap-drill size.

Lets say you have a 1/4-20 bolt.

You need to tap a hole for it to fit in, but don't know the tap drill size.

No problem.

Take the pitch of the thread( in this case 20) and divide the pitch by one.

1 divided by 20 is .050 or 50 thousandths.

Take the diameter of the thread( in this case .250) and subtract the .050 for a total of .200.

That is your tap drill size.

It works well and is always within a few thousandths of the standard tap drill charts. The standard tap -drill size for a 1/4 -20 thread is a number 7 drill bit..which is .201 diameter.

Lets do another.
a commonly used size 3/8 -16.

1 dived by 16 is .0625.
.375 -.0625= equals .3125 or 5/16 drill bit. Guess what? The tap drill size for a 3/8-16 is a 5/16 drill bit.

Amazing isn't it?


thanks, I learned something......

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