Analog film photography and cameras

Does anyone know of a lens fitting that is similar to M42 but not quite the same thread pitch? I have an old lens that screws into my Zenit about one turn but won't go any further - neither thread is damaged and my other lenses screw in fine. Also, according to the scale marked on the focusing ring reads from 3.5m - 30m - infinity, but in reality it won't focus on anything under under about 12m away - not very useful, it doesn't seem to be broken in any way, is this normal/to do with it not screwing in properly? The lens is an old Promura 135mm 1:3.5 lens, if that helps.

Sounds like its T-mount - is a 42mm thread but with a 0.75mm pitch rather than 1mm that m42 has - normally used for telescope mounts iirc