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  #1  
Old 03-06-2008, 10:03 AM
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Dust Dust is offline
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Default How to thread NPT holes

"American Standard taper pipe thread" = NPT

Well, again i received some great info from my vari buddy - proper procedure for cutting pipe thread holes

minimum requirement for material is 3 threads, so if you have a thread that is 27 per inch, for three threads you need 1/9th inch, or 1/8th minimum.

for me - i would always go slightly bigger and probably use 3/16ths.

Next - use the first third of the tap and don't forget tapping fluid, NOT oil - oil does the opposite of what you want to do in tapping, and then put the part in the hole. Count the complete turns that you get.

you want three. If you do not get three turns, put the tap back in and when it starts cutting count the turns for the number you were missing. if you got 1.5 turns, then go 1.5 turns more.

Simple as that. Wish we would have known that 8 years ago

enjoy
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Old 03-06-2008, 02:56 PM
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Default Re: How to thread NPT holes

Drill size for tapping pipe threads

Size Taps
(inches) Thread
(inches) Drill
(inches)
1/8 27 21/64
1/4 18 27/64
3/8 18 9/16
1/2 14 11/16
3/4 14 29/32
1 11 1/2 1 1/8
1 1/4 11 1/2 1 15/32
1 1/2 11 1/2 1 23/32
2 11 1/2 2 3/16
2 1/2 8 2 9/16
3 8 3 3/16
3 1/2 8 3 11/16
4 8 4 3/16
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dust

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Old 03-06-2008, 08:08 PM
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Default Re: How to thread NPT holes

wish i'd had that post 28 weeks ago!
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edited by steve for a good reason
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Old 03-07-2008, 11:31 AM
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Default Re: How to thread NPT holes

Code:
NPT Size	*Tap Drill Size (in.)	Decimal Equivalent (in.)
1/16 - 27		"C"				0.242
1/8 - 27		"Q"*				0.332
1/4 - 18		7/16				0.438
3/8 - 18		9/16				0.562
1/2 - 14		0.703125			0.703
3/4 - 14		0.90625			0.906
1.0 - 11•1/2	1•9/64			1.141
1•1/4 - 11•1/2	1•31/64			1.484
1•1/2 - 11•1/2	1•23/32			1.719
2.0 - 11•1/2	2•3/16			2.188
2•1/2 - 8		2•39/64			2.609
3.0 - 8		3•15/64			3.234
ok that is the best i can format it!

Now off to the store i go to get darn leterr'd drills - only have fractional and numberred
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Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world

Last edited by Dust : 03-07-2008 at 11:53 AM.
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