The OPPRESSOR family is multi-caliber compatible with .223/5.56, .308/7.62 and 9mm calibers. The Strike Industries OPPRESSOR Universal is a blast shield that works with almost any muzzle device on the market that has a maximum outer diameter of 25.00mm (0.98). This OPPRESSOR U version works just like the rest of the SI OPPRESSOR family and redirects blast and sound while maintaining the recoil reduction of muzzle devices. Designed with a SI proprietary 3-lug quick detach base, the OPPRESSOR Universal is easily installed and removed with a push and a slight turn. Install SI OPPRESSOR Universal 3-lug QD base, the included correct sized crush washer, properly set the timing/alignment of your muzzle device and you are ready to go. The OPPRESSOR U is made of a steel core with a 6061-T6 aluminum body and is anodized.