These are a bilock style, made for 3 lug 9mm, 40, & 10mm MP5 style barrels. It will fit both a threaded or non threaded 3 lug muzzle. The fake suppressor portion is made from one solid piece of Billet Aluminum. The internally threaded adapter that connects to the 3 lug is made from steel.
When permanently attached to an MP5 9mm style barrel they will bring the overall barrel length over the 16″ minimum. Can also be used as a display piece without permanent attachment.
The extensions are fairly light (12.5 ounces) and designed so they will not degrade accuracy.