Harrell's “Tuner” Muzzle Brake. 0.985 outside of brake body (where the vent holes are). I am unsure of the thread and pitch. The minimum inside diameter of the treads is 0.580 inch. It was installed on a “Heavy Varmint” contour barrel. It was installed on a .22 wildcat barrel. I wore out the barrel so the brake is available. Laser etched micrometer scale. Knurled finger tightened lock nut. All stainless steel. More photos, of different angles, if you send your e-mail. I prefer PayPal. $50 delivered.