Yankee Hill Machine 4401MB28 sRx Mini Muzzle Brake. Quick-detach sRx Mini Muzzle Brake designed for use with Yankee Hill sRx adapters. Thread pattern is 1/2-28 tpi. Finishes include Phosphate on Steel construction. Compatible with YHM-4400 adapters. The Mini Muzzle Brake adds minimal length and weight while enabling the sRx system performance for a compact muzzle device.