It is one of the tools used for relieving the jamming of a drilling tool. It releases the jam by loosening the jamming point with intensively jarring force.

The surface bumper jar is a mechanical impact tool installed between the hook and swivel or top drive and drill string, designed to deliver downward impact forces to free stuck pipe during fishing operations. Manufactured in compliance with API Spec 7K, this tool utilizes a splined mandrel and hammer assembly that stores energy when the drill string is rapidly lowered, then releases it upon sudden deceleration to generate a powerful downward blow. The surface-mounted configuration allows the driller to observe and control jarring action directly from the rig floor, enabling precise impact delivery without tripping the drill string.