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"1/2 NPT" drill and tap sizes?

50K views 16 replies 10 participants last post by  Suprafied 
#1 ·
I need to drill and tap some 1/2 NPT holes, anyone know the drill and tap sizes?

I asked the tool guy at Sears and he just looked at me like i had boobs on my forehead. :scratch:
 
#2 ·
Technically a 1/2 NPT should be a 45/64" drill bit. However an 11/16" is the next closest I believe.

Use this site fir a future reference.

http://www.korit.com/tapndrill.htm
 
#7 ·
The correct bit for any tap should be 90% of the tap size.

NPT requires an 50% increase adjustment since it is measured differently than drill bits.

Therefore, 1/2 * 1.5 (50% increase) = 0.75
0.75 * 90% (tap to drill bit conversion factor) = 0.675

Drill bit sizes in that range
21/32 = 0.6563
11/16 = 0.6875
23/32 = 0.7188

11/16 is the closest and the correct size for that tap.
 
#10 ·
Gadfly said:
I asked the tool guy at Sears and he just looked at me like i had boobs on my forehead. :scratch:

Do you? Pics?
 
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