I was working on the mower and needed to refresh the threads on a 3/8NC wing nut. There was a bin of taps nearby that I had picked up at a garage sale, but hadn't sorted into my bins that seemed to have the right tap. The first one I picked up said 3/8-16 on it, but it wouldn't fit in the old threads, so I set it down and grabbed another that also said 3/8-16 and it fit, so I ran it through and worked well.
I picked up the first tap and looked at it closer, seeing below the 3/8-16 it said Helicoil. So I put it with my Helicoil sets.