Strange. I copied it directly from their site. Just tried again, but fro some reason the link doesn't work when I copy it directly from their site. Mine is 1/2x20 threaded model. The link above from cilami is a the push on model. It's easy enough to find on their site. No idea why the link doesn't work.
This gun is on my short list of Bull pups to buy. I spent way way too much money on shotguns last bird season or I would have already bought this one. Great looking gun!