These collars are made of steel with black oxide finish and include the hex wrench as shown in the main photo. They grip tight and even without damaging the surface they are clamped to. 

 The 7/16" collar fits standard Crosman 7/16" barrels. It can be used as a cutting guide for shortening barrel length or one or more can be used as weights to reduce muzzle lift. These have one screw that tightens to clamp tight around the barrel. This style tends to clamp on more square than the two-screw style. Fits a 7/64" hex wrench, not included but is available in the Hex Wrenches listing. 

 The 3/4" two-screw collar fits 22XX, Discovery, Maximus, Marauder Pistol and similar valves. It fits a 3/16" hex wrench which is not included but available in the Hex Wrenches listing. I use these to make assembly/disassembly easier for valves with harder o-rings or threadlocker. I do not recommend using threadlocker on valves. It's sometimes on CO2 valves from the factory but not always. The one-screw collars shown on the valves in the photos are no longer available.