Aero's gas blocks create an efficent and reliable gas system for your AR15 or AR 308 rifle build. Features fits barrels with .625 outer diameter, low profile for easy fitment and set screws are steel 10-32 x 3/16 knurled cup point.*Note- Roll pin not included. We do not recommend the use of red thread locker on the threads of the set screws. If you decide to use thread locker we recommend using the non permanent variety. Made in the USA.