I don't have one, but I'm almost sure it'll either be 1/4"-20 or 5/16"-18. I'd say 1/4" would be most likely, although I've had a couple Windlass swords that were 5/16". I'm not sure if CS is still getting these via Windlass, but I do know they're still sourcing them from India, and all the India stuff I've run across uses Imperial threading, so I'd still say one of the above will probably be it.