FS Dynamic Resistance Muzzle Brake with 1/2-18 TPI threads for 5.56/.223 caliber
Used for a single 3 gun match with about 150 rounds
Manufacturer page here
New they go for 75.
35 dollars shipped. Will include crush washer.
PayPal FF, +4%, or USPS money order
Pics of actual brake for sale below (not a stock photo)