Well Workover Rig Disc Brake‑350 for 350 Workover Rig Hoisting System The XJ350 disc brake actuator consists of the brake disc, working caliper (normally open caliper), safety caliper (normally closed caliper), and caliper frame, divided into service brake and safety parking brake. 1. Brake Disc Installation position: On both sides of the XJ350 drum axle, single-side wear limit 5mm. Structure: Air-cooled, friction braking reference surface. 2. Working Caliper (normally open