I have an Advanced Armament Copr. Blackout 90T MK13-SD Muzzle Brake, 5/8" X 24 tpi, includes timing washers. Was $120, now $100
Manufacturer specs here,
Mounted and used on my 700 Sendero but in great shape, no scratches, decided to go with Silencerco instead.
Located on Beacon Hill, PM for best contact, Photos up soon.