Mounting a 135mm Componon-S

I recently purchased a second 135 Componon-s to set up a second enlarger. The first one I had came on a lens board already mounted (Beseler 45MXT) using the heavy collar with the set screw. The second one came mounted with a small ring and the heavy collar below the lens board. Is one way right and the other wrong. It seems using the heavy collar as a retaining ring, the rear lens cell cannot screw down completely. That being said, it has been printing just fine.

Anyone want to offer an explanation? I might just call Schneider.

You need a retaining ring.

You can buy the generic retaining ring from Adorama. Check the specs at Schneider (I think that's where I found them) for the correct size.