In trying to repair an old Zeiss Nettar 515/2, I went to my bag of goodies to pull out a new/old stock shutter to replace what I assume is a Prontor #0 shutter that has serious damage. My replacement is new/old stock and says Prontor at the bottom. Speeds are 25,50,100,125,B, and T. The shutter in the camera looks very similar but goes 1sec. to 150 and has no T. It says "Klio" across the bottom but has the Prontor logo. In the process of exchanging, I found that, while the Klio has threads at front and back that are the same (approx.29mm,) my replacement has 29mm threads with a different pitch on the front and 26mm threads on the back. I've not found any reference to different size threads on Prontor shutters - especially ones that are simply labeled "Prontor." SK Grimes site has the #0 size as having 29mm on front and rear. Clearly, Prontor shutters were sometimes custom made for particular lenses. (This one has never been mounted and has no aperture scale on it.) Am I going to have to shop carefully to finds a replacement or have I got the only weird Prontor that anyone has seen in having 29 and 26mm threads?