1.200 or larger on the shank. It's for a WTO switch lug on a lone peak fusion. I would like a 10 twist so I can run 250 and 300's. I'm wanting to do a short barrel like 20" I have a long 338 Imp. Barrel so looking for a short hunting barrel that I can get 2650 or do out of a 300 or maybe 2800+ out of a 250 and it be reasonably light weight and maneuverable. I need probably an M40 or smaller diameter to fit my barrel.channel so any kind of rem varmint, Palma or the like would work