The 65644 is a torque cover. The torque cover is compatible with any of the TL-Series DC Electric Screwdrivers. A torque cover is an optional cover attached to your screwdriver, once your specific torque range is set. Once the torque cover is set in place the torque range can not be adjusted until the torque cover is released. Torque Cover #65534 (ES-Series Torque Drivers) and #65550 (AC-Series Torque Drivers) are also available.