Mech parts are sections of the mech's body, namely: its arms (arms), its legs (lower), its pelvis (middle), and its head/chest (upper). They are cosmetics that can be swapped out to give the mech a different shape and appearance than it would normally have.
There are two types of mech parts: those that can be bought with MC, and the "elite" parts that can only be unlocked by gaining mech ranks via gaining XP. The former can be applied to all mechs that share a weight class, while the latter can only be applied to the mech that was ranked up.
Notes: mech parts are not universal and are only unlocked for the mech that was selected in the garage when they were bought. This means if the player wants the same part equipped on several mechs, they will have to buy the part several times.
An asterisk (*) next to the part name indicates that this part will block out Paint Patterns applied to the corresponding area of the mech if it is equipped. This will not apply to Elite parts as they all block paint patterns by default.
The mech parts are referred to by their mech's codename. For players who are not familiar with said codenames, clicking on the links in the codenames of the vanilla parts in the "upper" section of each weight class will bring you to the mech's page with its common designation. Some parts do not correspond to any ingame mech. This is the case of the Nief, the Civ, the Hon, and all the unavailable/unreleased parts with the exception of the Cupcake.
Non elite C-Class mech parts can be equipped to any C-class mech. Note that even though C-Classes' "arms" are actually adjustable armour flaps on their back, that section of the cosmetics is still called "arms".