4 Vent Muzzle Brake  with Wrench Flats, 1/2 x 28 ID Thread
Precision machined from 4140 ordnance grade steel with black magnetite protective finish. 

Outside Diameter = .850"
Overall Length = 1.750"
Weight  = 2.6oz

Made in USA.

Photos taken with a 16" 5.56 barrel using 55 gr FMJBT XM193 - Federal American Eagle ammo