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Old 03-13-2008, 04:47 PM   #1
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Default Drilled pan hole is too small I'm an idiot

I have a 3/8 NPT to -8AN adapter to put in my oil pan. I went to Home depot and bought a drill and tap kit that came with a 3/8 tap which said on the back to use a 5/16" drill bit. Not thinking, I went out, just finished drilling it, and THEN looked at it and said to myself "my my that's a small hole..." sure enough, looks like 3/8 NPT means a 3/8 Inner Diameter and I just drilled and tapped a 3/8 diameter hole!

Sooo... what is the CORRECT size tap and drill bit size for a 3/8 NPT hole??
Also, where to find such a drill/tap? Because the 3/8 one I got which is way too small for the 3/8 NPT was one of the largest I was able to find - the kit I bought only goes up to 7/16...

Help please...
-Ryan
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Old 03-13-2008, 04:50 PM   #2
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9/16" or 37/64" IIRC.


make sure you got the right tap.... if it's like 3/8-16 or 3/8-24 it's not the right thing.
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Old 03-13-2008, 04:53 PM   #3
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yep 9/16 or 37/64

and its 3/8-18 npt i believe
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Old 03-13-2008, 04:54 PM   #4
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it should simple be a 3/8 NPT tap.

-16 or -24 would signify NC or NF threading, not NPT.
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Old 03-13-2008, 04:57 PM   #5
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Local industrial place says it's supposed to be a 37/64" drill bit and a 3/8-18 pipe thread tap (which is apparently very different in size from my 3/8 bolt thread tap)...

Can anyone verify this? Does that sound right?

edit: posted this before I saw a few more replies. sounds like I've got the rights sizes now. Are you saying I can use either a 37/64 or a 9/16 bit?

-Ryan
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Old 03-13-2008, 04:58 PM   #6
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yeah sounds right.
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Old 03-13-2008, 05:00 PM   #7
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Its either slightly bigger or slightly smaller then the tap, either of those bits will work.
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Old 03-13-2008, 05:03 PM   #8
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Quote:
Originally Posted by Braineack View Post
it should simple be a 3/8 NPT tap.

-16 or -24 would signify NC or NF threading, not NPT.
am i confused then?

http://www.fastenal.com/web/products...ex?sku=0326935
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Old 03-13-2008, 05:20 PM   #9
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no you're right -18 is correct. -16 and -24 isn't
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Old 03-13-2008, 05:22 PM   #10
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Usually, the proper drill size is written right on the tap.

C
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Old 03-13-2008, 07:02 PM   #11
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I used a 9/16" bit, seemed to work perfectly, especially since you have to drill at a slight angle because I know I couldn't fit my drill right on with my A/C in the way.
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Old 03-13-2008, 07:20 PM   #12
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I used a 9/16" drill as well, worked just fine.
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Old 03-13-2008, 07:46 PM   #13
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Perhaps if your profile included the city you live in, somebody local would chime in who could let you borrow one. Otherwise, most Nothern Tool stores have those sizes on the shelves.
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