Unusual 1/4-18 tap

why what's the problem? I read the details from my mullins thread wall chart. it lists the 18 pitch threads exactly as quoted.

the post answers the last two sentences of the question. a. what's it used for? - pipe thread. b. his suspicion that it was a mistake is probably wrong since there is a listed application for the thread size.

pilot notes .....pilot notes??? now what are they? a description of the machining standards for slocumbe drills?

Stealth :-) Pilot

You missed the fact that this thread in question is 1/4" diameter. It is *not* a pipe thread. It is a non-standard 1/4" tap.

Harold

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Out of curiosity -- what does the mullins thread wall chart say is the OD of the thread. IIRC, the original question said that the actual measured OD was 1/4", while any pipe thread would normally be named for something closer to the bore size, thus requiring a much larger diameter for the threaded part.

Not clear -- until you can tell us that your chart shows the OD as 1/4". It could easily be some other thread with the same pitch, but a smaller OD, for a different function.

Again -- are you sure about the OD?

Enjoy, DoN.

I wonder what that glow is around here?

11mm tapping drill for both.

oh I get it. the light's on.

Stealth Pilot

What is it about the following that you are unable of grasp?: From the OP:

"I know that is the designation for a standard NPT tap, but this tap is actually 1/4" in diameter."

Tom

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11mm divided by 25.4 mm per inch gives a diameter of 0.4331", and the actual tap diameter would have to be a bit over the tap drill size, while the original poster said that *his* tap was measured at 1/4" (that is 0.250" so these are *very* different taps.

Where? Not in your head, yet, apparently.

Enjoy, DoN.