SureFire Ryder 9 Fixed Barrel Spacer

Silencers can be threaded directly to the barrel or to a quick detach (QD) mounting system.

Hub Mount is an industry-standard rear thread pitch for suppressors. The HUB mount is 1.375x24 (1 3/8x24) and can accept any muzzle device in that thread pattern, regardless of the brand.

A QD mounting system allows you to quickly and easily install or remove your suppressor across multiple firearms equipped with the QD mount. The adapter attaches to the suppressor's rear threads and mounts to the muzzle device specific to that system, i.e., Dead Air Keymo adapters mount the Keymo pattern muzzle devices.

Direct thread silencers screw directly onto the muzzle threads of a firearm, making it the simplest mounting system and saving on added weight and length. QD systems include provisions to attach the silencer faster, have a more secure attachment, and move the silencer easily to different guns.

Direct thread systems are generally lighter and shorter than QD systems, making your setup more compact and maneuverable. QD systems provide very secure attachment and the ability to easily swap the suppressor to different hosts. 

A pistol booster system is designed to allow tilting barrel pistols (Glock, Sig, Walther, M&P, etc.) to cycle properly with an attached silencer. They work by decoupling the weight using a spring and attach to your threaded pistol barrel using a piston.