If you’re into gears then you’ll need a front and / or rear mech (also known as derailleurs). All the big names in stock including Shimano and SRAM, for both road and MTB use. Clamps and shims too! Front mechs can be top pull or bottom pull, and top swing or bottom swing. Check your cable routing to ensure compatibility. Dual pull front derailleurs are compatible with both systems. It is also important to check the actuation ratio matches your shifters (1:1 or 1:2), and that your rear derailleur matches your shifter, cassette and chain (9 or 10 speed).