In article ,
Richard J Kinch wrote:

There's an odd thread, called the Leica thread, that is used on
photographic enlarger lenses. It is specified as 39mm in nominal diameter
but 26 tpi in pitch.

I'm wondering what other monstrous metric-English combinations are out
there?

I could send you about 5# of 1-1/2 inch long HHCS in 1/4-20 thread with
10mm heads.

And they ain't bad 6mm X 1.0s either. They're real honest-to-God 1/4-20.

God alone knows where those came from. I've never seen them as original
parts on any of the wheelchairs come into our shop. Been some chairs go
out with them though.