Features and Benefits:Works on hard to reach idler pulleys;Releases Tension on Serpentine Belts With a Spring Loaded Idler Pulley. This tool is used to remove and install belts on serpentine belt systems using the spring loaded idler pulley. Forapplications with limited access, 13mm and 16mm sockets are built into the handle. This tool covers most domestic and some import applications. Comes with extension for hard-to reach idler pulleys. Nine low profile sockets and extension help to fit into tight spots.