I had to use a couple of adapters to fit my Cokin 'A' series filter holder to the 101mm f4.5 Ektar lens of my Mini Speed Graphic. Since this lens doesn't have a threaded barrel, I first had to find a push-on Kodak 1 1/4" to Series VI adapter (which is about 44mm). I was able to get both the push-on with a filter retaining ring, which allowed me to glue in a 43mm to 49mm adapter just to the retaining ring. This was the closest to 44mm I could find, so it was a bit too loose & required the glue to bond it properly. I already had a 49mm Cokin adapter that snapped right into the Cokin 'A' filter holder. The A series Cokins are much smaller & a bit more difficult to find these days, but for my smaller 2 1/4 x 3 1/4 camera, the 'A' size was the best fit and I now have both Polarizer and Red (A003) filters to work with for my intended B&W shooting. This combo can be seen on camera at my profile page. Word of warning though, be gentle with the old Kodak push-on adapters since they are getting hard to find and be sure to measure CAREFULLY before buying one without trying it on your lens! A bit of head-scratching and research (& a few $$), but this set-up turned out very sturdy and smooth... and of course, I now have an unlimited resource of Cokin filter possibilities. Good luck!