A variable adapter for barrels that are not threaded.
The variable adapter is simply pushed onto the end of the barrel & tightened in place with the thumb screws. NateChrony Variable Adapter - 14-25mm, Black (If you destroy one adapter, put the screws on the other & you're good to go!) Thumb screws are high quality stainless steel so will never rust. Price is for 2 adapters, with 1 set of screws. The bore & outer barrel MUST be concentric! The adapters can be adjusted from its maximum diameter down to the minimum diameter.