Releases tension on serpentine belts with a spring loaded idler pulley. For applications with limited access, 13mm and 16mm sockets are built into the handle. Comes with extension for hard-to-reach idler pulleys. Includes 9mm socket for Honda and Toyota applications Fits idler pulleys requiring 13mm, 14mm, 15mm, 16mm, 18mm, 19mm hex and both 3/8" and 1/2" square drive sizes.