Don Young wrote:
Going through some old taps I found a tap marked 1/4"-18. I know that is the
designation for a standard NPT tap but this tap is actually 1/4" in
diameter. Looks like a 1/4"-20 with coarser threads. Does anyone know of an
application for such a thread? I suspect it might have been made mistakenly
from a list of sizes which included the pipe thread. No manufacturer
identification and appears to be a cheap import quality.

Don Young


Had a look in a cat and 16, 18, 20, 22, 24, 26, 27, 28, 30 and 32 tpi taps
in 1/4" size, were in common supply, once.

Tom