RC 1/8 Threaded info.?

Question

What is the drill size ?

What is the Pitching ？

Can someone help to solve ?

Answer 1

RC is an ISO std.  in short,...

Rc: Series British Standard Pipe - Taper- BSPT,

ref: http://www.newmantools.com/taps/bsp.htm

28 TPI

tapping drill is 21/64" (see half way down the page).

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NPT, BSPP and BSPT are all different threads.

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Answer 2

Are you sure that's what the thread is called?

The 1/8 National Pipe Taper(NPT) is 27tpi and the tap drill size is letter R.

There could be several pitches for a straight 1/8 thread.  They would each have a diferent tap drill size.  To find it you subtract the pitch from the nominal size or look it up on a drill chart.