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NSP threads - what drill bit size ?
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mgb
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PostPosted: Mon Jun 04, 2007 12:03 pm    Post subject: NSP threads - what drill bit size ? Reply with quote

Hello

I would like to make a couple of threaded holes to take a 1/8" and 1/4" NSP adapters, could you please tell me what size drill bits I should use.

Many thanks

Mike
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Uncle Joe
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PostPosted: Mon Jun 04, 2007 1:36 pm    Post subject: Reply with quote

First off, they are called NPS, not NSP. Assuming you are not asking for a taper thread, then the ABSOLUTE correct sizes are:

For the 1/8-27 size, use drill size S.

For the 1/4-18 size, use 29/64.

If you dont have these drill sizes, and not many people do! Very Happy its possible to use an 11/32 for the smaller, and a 7/16 for the larger....

NPS is an American standard, are you sure they arent BSP?

UJ
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Rick
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Joined: 27 Apr 2005
Posts: 21314
Location: North-west UK

PostPosted: Mon Jun 04, 2007 2:20 pm    Post subject: Reply with quote

hi MGB, welcome to the site (and thanks UJ for providing the info)

Rick
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Rick (OCC Admin)
Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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Uncle Joe
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PostPosted: Mon Jun 04, 2007 2:23 pm    Post subject: Reply with quote

Yes, welcome to the forum, mgb.

Rick, its nice to know someone appreciates me... Laughing
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mgb
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PostPosted: Thu Jun 07, 2007 7:02 pm    Post subject: Reply with quote

Many thanks UJ for the info and to Rick for the welcome.

I got the name of the thread wrong, it should have been npt and I think that it is a tapered thread. I am fitting a fuel pump union to a tank along with a couple of extra unions for a level guage.

Always thought there was a bit if dsylxeia in there somewhere

Cheers

Mike
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Uncle Joe
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PostPosted: Thu Jun 07, 2007 8:04 pm    Post subject: Reply with quote

Do you want the info for NPT? Being the mine of information that I am...

UJ
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mgb
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PostPosted: Thu Jun 07, 2007 11:22 pm    Post subject: Reply with quote

Yes please, that would be a big help
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Uncle Joe
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PostPosted: Fri Jun 08, 2007 7:59 am    Post subject: Reply with quote

Taper threads are a little more difficult to do at home. If I didnt have the tools, I would give the job to a small local engineering company. If any still exist!

For the 1/8" use an R-size drill, follow up with a 1/8NPT Taper Reamer, then tap.

For the 1/4" use a 7/16 drill, follow up with a 1/4" NPT Taper Reamer, then tap.

Do not miss out the reamer step!

Let us all know how you get on.

UJ
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mgb
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PostPosted: Fri Jun 08, 2007 12:12 pm    Post subject: Reply with quote

Many thanks

As I only have 3 holes to do, I think I will take it round to my local engineering firm

Cheers

Mike
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Uncle Joe
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PostPosted: Fri Jun 08, 2007 1:07 pm    Post subject: Reply with quote

If you tell us more about the particular job, then there might be other solutions to suggest.

UJ
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mgb
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PostPosted: Fri Jun 08, 2007 2:48 pm    Post subject: Reply with quote

I am making a petrol tank out of a fire extinguisher case for my autotest car, I have a brass union with an 1/8" npt thread for the outlet and 2 brass 90 degree unions with 1/4" npt thread. One of the 90 degree unions will go at the top of the side of the tank, the other at the bottom, with a length of petrol resistent clear plastic tube between them.

The walls of the tank should be thick enough to drill and tap - hence the question.

Cheers

Mike
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