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