8pcs Serpentine Belt Tension Tool 3/8" Idler Pulley Wrench Crow Foot Socket Set. 3/8" Drive Crow Foot Wrenches 13mm, 14mm, and 15mm. 3/8" Drive 6 point Sockets 15mm, 16mm, and 18mm. Kit Includes This kit also will work on idler pulleys requiring 15mm or 18mm Hex, and 3/8" or 1/2" Square Drives.