While on vacation, I picked up a few odds and ends in antique/junk stores, and found an cheap old Soligor 100-200mm pre-set lens. It has the spiffy chrome and black striped focusing, aperture, and zoom rings, so I had to have it. It has a Petri t-mount with rear cap that screwed off easily. But when I went to put a Nikon t-mount adapter on, it wouldn't screw on . I tried several t-mount adapters I have for other lenses, and none of them worked. One of my older ones started to take hold, but jammed after maybe one turn. I know that t-mounts have a 42mm thread size, so I measured the thread size on the lens, and it looks to be about the same, including the thread pitch, but it seems to be just a little too big for the adapters. (I don't have anything more accurate than a steel drafting ruler) The threads don't appear stripped at all either. So I don't know what's going on here. Were t-mounts ever made in other sizes, like 43mm? I have never seen a pre-set lens use anything except a t-mount adapter. Anybody have any experience with these things? Any help would be appreciated.