Can someone identify this mount?

[jpentecost]

I found this adapter in a box of "stuff" and the other end is a regular M39 mount but the thread is reading at about 30 1/2mm which would say 31mm or so in my mind ... Is this possibly a darkroom item ? I remember a Gnome Enlarger as a child having a smaller than M39 Mount mount ..

 

[gone]

It could possibly be used for extension tubes? That 31mm size is pretty unusual, I got zero hits on google by searching for enlarger lenses w/ that size threads. All I saw was a 31mm lens to Series 6 adapter, but that looked to be OD, not ID.

 

[Ian Grant]

My early post WWII Gnome enlarger has an M39 thread. Schneider Componon lenses pre the S series had a smaller mount and came with M39 adapters. I acquired a Wray 50mm recently and that is a smaller threadmoint.

Ian