Shimano SL-M951 is a high-performance rapidfire SL shifting system designed for mountain bikes. It features smooth and precise shifting with minimal effort, allowing riders to change gears quickly and easily. The SL-M951 is compatible with Shimano's XTR SIS-SP40 sealed outer casing and bottom bracket cable guide for optimal shifting performance. It also has a low-friction design that reduces cable resistance, making shifting even smoother. Additionally, the SL-M951 is easy to install and adjust, making it a great choice for riders of all skill levels.