Ultradyne USA APOLLO Brake, 5.56MM/223REM, Fits AR-15s with 1/2X28 Threads, Black, 4.4 oz., 416 Stainless Steel, Includes Shrouded Timing Nut UD10680 APOLLO MAX sets the standard for performance by providing breakthrough recoil reduction and unparalleled muzzle compensation for those who refuse to settle for second best. Gases are strategically diverted away from the shooter and out of the shooters line of sight. Experience smooth" on-target recoil compensation in a competition-legal package. Minimum barrel length for the Apollo Max is 16". Like all Ultradyne muzzle devices" a timing nut is included for easy installation.