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. The bore & outer barrel MUST be concentric! Otherwise damage or injury could occur. Select the maximum outer diameter of the barrel from the options. The adapters can be adjusted from its maximum diameter down to the minimum diameter. Thumb screws are either high quality stainless steel, or lightweight aluminium, so will never rust. Price is for 1 adapter, with 1 set of screws.