Wollensak 135mm f/4.7 Raptar filter size?

I am trying to figure out what type of filters my Wolly 135mm f/4.7 Raptar takes. 37mm is too big and 34mm is too small. One of my co-workers suggested that it takes Series filters and I think he is on to something. Any idea what Series # filter this would describe? Also, where would I find these filters, infrared in particular?

- Justin

Series VI filters are about 41mm, so that should fit. Most of my press camera lenses take some form of Series VI adapter. Now you just need to find the push on holder which will probably be around 1 1/2 inch. If you can give me the exact outside diameter in inches I will see if I have a spare.