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Old 07-22-2010, 01:07 AM
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Nitrous tap & drill size

What size drill bit should I use to drill the holes for a standard nitrous tap (1/16 -27 NPT)?

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Old 07-22-2010, 03:41 AM
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Quote:
Originally Posted by 454headache
What size drill bit should I use to drill the holes for a standard nitrous tap (1/16 -27 NPT)?
That requires a letter size "C" drill bit or 0.242
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Old 07-22-2010, 05:12 AM
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Go HERE to see a complete tap & drill chart.

For 1/16-27 NPT it shows the drill size to be a 'D' (.246) drillbit.
For 1/8-27 NPT it show the drill size to be a 'R' (.339) drillbit.

I mention both sizes here because a 1/16-27 NPT is not a common size and more than likely the 1/8-27 NPT is the size you will be using.
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Old 07-22-2010, 05:35 AM
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HERE they recommend a 17/64" drill size.

HERE Holley recommends a 1/4" drill bit. And again in the NOS installation instructions HERE.

HERE, they say:
Tap size- 1/16"
Threads per inch- 27
Drill size w/ taper pipe reamer- 15/64"
Drill size w/out taper pipe reamer- "D"
Straight pipe threads- 1/4"

Last but not least, HERE they recommend a "C" (0.2420") bit.

So, choices are (in inches, except C):
0.2656 (17/64)
0.250 (1/4)
0.2420 (C)
0.2343 (15/64)

If I were drilling/tapping aluminum I would use a smaller bit and back the tap out often to clean it. Steel I would tend to use a slightly larger bit.
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