In message ,
misterroy writes
Can plug tap sometimes mean second and sometimes bottoming?

Here is RS's plug taps selection, some of them look like they get close
to the bottom, others less so.
https://uk.rs-online.com/web/c/hand-...threading-taps
/?applied-dimensions=4294885797

The names seem to vary from website to website.

Is there a definitive answer?

I rather think things have moved on since my 6 weeks in the apprentice
school 1960 or so.

We were shown how to drill holes and tap threads. Electrical component
manufacturer so we learned a lot about BA threads:-)

Hand taps came in packs of 3 (first, second and plug). Looking back,
they were made of carbon steel and rather brittle. Half turn forward and
quarter back to break the swarf.

I think the idea of the taper was that the tap would follow the hole
rather than cut the thread at an angle. The second tap followed the
threads formed by the first cut. The plug tap was only used if the hole
had a bottom.

Modern stuff is much stronger with better control of hardness. I suppose
RS assume their market is manufacturing where machine tools will ensure
threads are cut parallel.

ta

--
Tim Lamb