The GEM KALS Limit Switch for BH-USA A-Drive is to be used with a BH-USA A-DRIVE. Limit switches are for models ending in an “A” which denotes auto stop capability. Pre-wired for auto stop but only have this capability when used with the correct Gem Remote. Simply remove the dust cover on the front of the A-Drive to expose the end of the drive shaft that will have a tab that fits the limit switch. The GEM KALS Limit Switch for BH-USA A-Drive uses the existing bolts to mount the special bracket. Limit switch ready drive shaft is a must have.