Ultradyne USA ATHENA Linear Compensator, 5.56MM/223REM, Fits AR-15s with 1/2X28 Threads, Black, 3.8 oz., 416 Stainless Steel, Includes Shrouded Timing Nut UD10660 ATHENA allows a shooter to inexpensively upgrade their rifle to the Dynamount Sighting System. Muzzle rise has been optimized as well" with gas vented at an angle then forward. This sends a lower percent of sound back towards the shooter" optimizing sonic performance over recoil. Like all Ultradyne muzzle devices" a timing nut is included for easy installation.