Commercial Opener Garage Door Operator
Open the electrical enclosure and you'll find two Linear limit switches mounted to the V bracket. There's the Reverse Cutout Switch (A) and the Open Limit Switch (B). The limit switches are activated by the two limits nuts on the threaded shaft as the operator open and closes the door. When a limit nut nears the end of the shaft it activates a switch which sends a signal back to the motor control board to stop the door. Please reference your garage door opener manual for proper replacement and adjustment of the limit switches.