Features and Benefits:Designed to release the tension on spring-loaded idler pulleysMade in U.S.A.Sizes: 13mm or 1/2 in. hex, 14mm hex, 15mm hex, 16mm or 5/8 in. hex, 17mm hex, 18mm hex, 19mm or 3/4 in. hex, 3/8 in. square, 1/2 in. square, 3/4 in. square....(more info)