This part is used on Shimano Shadow rear derailleurs starting 2013. Will fit a cassette size of 40t or bigger. Improves shifting performance on 1-10 systems. Increases chain wrap, eliminates the need to drastically thread in the b-tension screw. Replaces the Direct Mount link on 2013 or later Shimano 10-speed Shadow+ rear derailleurs to reduce premature shifting degradation. Works with any 11-40 t or 11-42 t 10-speed cassette. Bolt included.