Quote Originally Posted by shutterfinger View Post
The threads in the front of lens made up through the 1950's maybe the 1960's are for the front element retaining ring only. Filters were made in series sizes IV through IX. Adapter rings for each series size were made in fractional steps for the various different sized lens barrels of the front lens group.
Series IV- 8mm and 16mm movie cameras
Series V- 3/4-1 3/16 inch
Series VI-1 1/4-1 21/32 inch
Series VII- 1 11/16-2 inch
Series VIII- 2 1/16-2 5/8 inch

Measure the outside diameter of the lens front lens barrel and look for a Series filter adapter that the measurement of the lens matches and series filters or as E says have a machinist custom make a threaded adapter. Some series adapters were marked in millimeters so convert the fraction to decimal and multiply by 25.4
Actually, most of these lenses - and the Turner-Reich specifically, but old Dagors, etc have no retaining ring in front. The threads might have been used during manufacture, for instance to hold the brass cell onto an arbor.