The Gas Blocks from Aero Precision come in various sizes and finishes, as well as being engraved with the Aero Logo or just plain. Fits barrels with .625, .750, .825, .936OD's Constructed from 4150 hardened steel Phosphate or nitride coating Low profile for easy fitment Set Screws are Steel 10-32 x 3/16 Knurled Cup Point Made in the USA Roll pin not included Please note: 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." Mfg: Aero Precision