tap hole size clarification

[maremsk1]

This may be a really basic question, but I need to thread a hole and am confused on the tap sizes. Im adding a telltale and the instructions state to use a 11/32 inch hole and a 1/8 inch tap. Before I buy a 1/8 inch tap, wouldnt that be way too small for a 11/32 inch hole?? Or am I missing something here?? Any help would be appreciated.

 

[minuteman62-64]

Re: tap hole size clarification

Maybe the instructions are referring to a tap for 1/8" pipe. 1/8" pipe has an OD of 0.405" and the tap for it (by my chart) requires a "Q" drill, which is 0.332" diameter. That's in the ball park of an 11/32" drill, which is 0.344" diameter.

 

[nwcove]

Re: tap hole size clarification

sure its not a 3/32 hole and the 1/8 tap?? those numbers definitely dont jive?

 

[Daviet]

Re: tap hole size clarification

All the tell-tales I have installed used a 1/8" PIPE tap for the fitting.

 

[maremsk1]

Re: tap hole size clarification

OK, I found a 1/8 tap and it looks to be about the same size as a 11/32 drill bit. So I guess the instructions are correct. I still dont know what the 1/8 means cuz its definately not the diameter of the tap. I figure minuteman is correct about the pipe size. The wierd thing is that all the other taps in the kit (like the 1/2) are sized acording to thier actual diameter. Just the 1/8 is goofy. Go figure. Well, Im going with the 1/8 tap and the 11/32 drill bit, and all looks good so far. Thanks guys!

 

[WernerF]

Re: tap hole size clarification

Here are the NPT diameters and threads:
http://en.wikipedia.org/wiki/National_pipe_thread