Yankee Hill Machine Yhm Low Profile Flash Hider 5.56mm For 1/2x28 Threads. 75" to be installed/uninstalled without the removal of the flash hider. Specifications for Yankee Hill Machine Yhm Low Profile Flash Hider 5.56mm For 1/2x28 Threads: Type/color: Low profile flash hider Size/finish: 5.56mm (1/2x28")/melonite Material: Steel Ar-15 accessory: Y Other features: Allows gas blocks with an inside diameter of .75" to be installed/uninstalled without the removal of the flash hider