I have a 3/4" NPT fitting I need to use. What size drill bit and tap do I need to get? Whats the difference between the 3/4-10 and like 3/4-16 taps etc..
Thanks
Thanks
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Drill bit and tap size
- Thread starter dmaxn04
- Start date
10 and 16 are threads per in. for corse/fine bolt threads. 3/4NPT= 29/32 drill bit. Drill bit sizes for NPT are 75% of the (NPT) tap size.
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NPT threads are tapered pipe threads, and you need a NPT tap only. There are "straight thread" pipe threads, but they are rare. If the tap says 3/4"-NPT that's what you want. I don't have my drill chart handy, but 29/32 sounds right. Get one that has a 1/2" shank.
When you tap and drill, you will want to use oil. Tap it down about 1/2 way down the tap, blow out the threads, then test fit. If you tap too far down with NPT threads, you wrecked the part. On elbow fittings, you can set where the elbow points during tapping, by test fittings.
When you tap and drill, you will want to use oil. Tap it down about 1/2 way down the tap, blow out the threads, then test fit. If you tap too far down with NPT threads, you wrecked the part. On elbow fittings, you can set where the elbow points during tapping, by test fittings.
Just so we are on the same page, heres the fitting I bought. I need to know what size drill and tap to use to tap a piece of metal. Its a 3/4"NPT fitting.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230328690435&viewitem=
I was looking online trying to find the size drill bit and tap.. I came up with a 59/64" drill bit. Is that right?
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230328690435&viewitem=
I was looking online trying to find the size drill bit and tap.. I came up with a 59/64" drill bit. Is that right?
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Yes the tap mentioned above and a 3/4 npt tap. The tap will say 3/4 npt on it. Tap it some and test the thread. It should screw in 3 to 4 full threads by hand before it gets tight. If it does not get to 3 threads then tap a little deeper. Once you reach that it should be perfect. apply some thread sealant compatiable to what is going to go through the line and your set. In the trade it is usually 3 1/2 turns to be right. Sprinkler Fitters aka Puzzle Fitters go about 4 to 5. TheyThey like to crank in there pipe fittings.
Brian
Brian
In post #2, I gave you the drill bit size my bit/tap chart shows! 59/64 is the next size larger drill bit FWIW.
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Ok thanks.. I ordered the 59/64 earlier. Guess I need to order a 29/32 also..
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I think he is doing a DIY twin setup so i would assume he his tapping the oil drain , unless this is for another project ?
OK, here's the thing with drill sizes for NPT:
Since NPT is tapered, the tap is going to cut 100% threads. Any drill bit that will allow the tap to start is going to work. The bigger the drill, the less work you have to do.
For thin-wall areas, use a drill on the high side of the recommendation, since it's going to seat the thread on the entry. For thicker pieces, go for the low side of the tolerance so the inside threads are still 100% for a better seal. I almost always go with the bigger drill. How can you tell you went too big? The threads won't come to a point. In that case, tap deeper until you get a 100% thread.
Since NPT is tapered, the tap is going to cut 100% threads. Any drill bit that will allow the tap to start is going to work. The bigger the drill, the less work you have to do.
For thin-wall areas, use a drill on the high side of the recommendation, since it's going to seat the thread on the entry. For thicker pieces, go for the low side of the tolerance so the inside threads are still 100% for a better seal. I almost always go with the bigger drill. How can you tell you went too big? The threads won't come to a point. In that case, tap deeper until you get a 100% thread.
Taping a piece of steel for my turbo drain.. Thanks.. I ordered the 59/64 and tap.