FOX FLOAT REAR SHOCK VOLUME SPACER KITChanging volume spacers in your shock is an internal adjustment that allows you to change the amount of mid-stroke and bottom out resistance. If your sag is set properly on your bike but you're either using too much travel or not enough travel, then you could install the proper spacer to increase your shock's performance. Fox Part Numbers803-01-250: Float DPS/CTD (9mm Shaft)803-01-251: Float X/DPX2 (1/2" Shaft)803-01-139: Float X2 | Fox Racing Shox | Float Rear Shock Volume Spacer Kit 2018-2021 Float X2, 803-01-139