This 3 Lug Mount replaces the piston assembly in your Obsidian9″ allowing you to attach the Obsidian9 to 3 lug compatible firearms. This mount is designed to be internal so that your overall firearm length is as short as possible. Using a 3 Lug Mount allows you to quickly attach/detach your suppressor to fixed barrel firearms, without having to worry about suppressor walk-off.