Although the thread OD is close to 29 mm, that’s not likely the actual design diameter. All of the Wollensak lenses I own or that I have measured for others have fractional-inch diameters and some integer number of threads per inch using 60° Unified V-thread as verified with my Lufkin thread-pitch gage.
For example, my162 mm f/4.5 Enlarging Raptar has 2” x 30 tpi thread.
Several Kodak and Wollensak enlarger lenses (both brands made in Rochester, NY) that I have measured have 1- and 3/8-inch x 30 tpi mounting threads.
My Wollensak 3 ½” f/4.5-32 Enlarging Velostigmat has 1- and 3/16” diameter x 40 tpi thread. It measures 1.1837” diameter, or 0.0038” smaller than the nominal diameter for assembly clearance.
A focal length of 3 ½” is essentially the same as 90 mm. Both the 3 ½” Velostigmat and the 90 mm Enlarging Raptar were made by Wollensak. It seems likely that both of these lenses of about the same size from the same maker would use the same thread. This is uncertain without an actual measurement of the lens in question. 1- and 3/16-inch x 40 tpi flanges or retaining rings are about as scarce as hen’s teeth now in 2019.
I’ve never encountered a 29 mm thread on any enlarging lens. Old (very old) Schneider 50 mm Componon lenses had 29.5 mm x 0.40 mm pitch thread according to some old Schneider data. See column C in the Componon data in the following link.
https://www.schneideroptics.com/info/vintage_lens_data/enlarging_lenses/enlarging.pdf
I have a very old Wirgin Wiesbaden Gewironar 1:4.5 7.5 cm enlarger lens with 29.5 mm x 0.5 mm pitch thread.
It’s often the case that folks use a ruler to “measure” an unknown thread diameter. Doing it this way is only an estimate. A proper measurement of a male thread must be done with a micrometer caliper with 0.001” or 0.02 mm resolution.
The thread pitch must be measured with a thread-pitch gage. It’s important to realize that the actual diameter of male thread is usually somewhat smaller than the nominal diameter due to the necessary assembly clearance.