Series 86 block and tackle is built for sideload sash applications in both residential and commercial windows and is rated class 2 on the aama verified components list, the north american fenestration standard (nafs). Series 86 is designed to allow for quick and easy installation or removal of the sash. Part# 17b42-40, 43" channel length, id stamps: 42-40, 42-4, 42-d