A perfect addition to your trailer's existing leveling or stabilizing jacks. The Lock-Arm extends to the trailer frame and mounts with two self-tapping screws (included). After the one time installation, the Lock-Arm will move up and down with the operation of the trailer's jack and will self store on the trailer. Once the jack is in the down position with the Lock-Arm extended, use your 3/4" crank handle to tighten the set bolt. This will secure the Lock-Arm and provide extra front to back stability. One pair of Lock-Arm Bars with mounting hardware per box. Will work with various styles and brands of jacks. Limited lifetime warranty.