The B&H site in NYC lists circular filters in sizes 34 mm and 35.5 mm. I wonder if the “35 mm filter” might be 35.5 mm whose size statement has been shortened to “35 mm.”
It would be useful to have someone measure the OD (Outside Diameter) of the thread with a micrometer or dial caliper.
A male 35.5 mm thread would measure slightly less than the named size, since the OD of male thread is marginally smaller than the nominal diameter for the necessary assembly clearance. For example, a 40.5 mm x 0.50 mm filter I measured has an outside diameter of 40.39 mm, or 0.11 mm smaller than the nominal diameter.
Using this differential, the named diameters and the likely measured diameters of three sizes close to 35 mm would be:
Nominal 34 mm, likely actual diameter 33.89 mm
Nominal 35 mm, likely actual diameter 34.89 mm
Nominal 35.5 mm, likely actual diameter 35.39 mm
If the size of the filter actually is 35 mm, it would be interesting to learn of the camera for which it was made. I poked about on the Internet but couldn’t find an answer.