MINI FLASH HIDER WITH 1/2X28 THREADS. THIS IS THE ONE WE USE WITH OUR HDD P90 COMBO DEVICE. THESE ARE FOR INSTALL ON ANY 1/2X28 THREADED MUZZLE SUCH AS AR15, SCAR 16 ETC.  INSTALLS WITH A 11/16" WRENCH AND A CRUSH WASHER.  MEASURES ONLY 1.450" LONG.