Thanks, Mike. I must have either had a major brain fart or the phone rang, or ...

After saying that all my Kowa lenses took 67mm, I meant to, and should have added, that this was not true for all Kowas ever made; and that it made a difference which model Kowa 150 the OP had. The older ones used different filters but Kowa standardized for most (not all) of their lenses later on is my understanding. Of course, I could be wrong ...

The simplest thing is just to measure the filter threads. Whichever model the lens is, it's going to be a readily available filter size.