PERFORMANCE TOOL W84010 Use To Release Tension On Serpentine Belts With Spring Loaded Idler Pulleys; With Handle/ Three Sockets/ Three Crowfoot Wrenches. ManufacturerPart : W84010. Use To Release Tension On Serpentine Belts With Spring Loaded Idler Pulleys; With Handle/ Three Sockets/ Three Crowfoot Wrenches.