The ZeroRC Hub-S-6-4 refers to a 4-piece set of "Narrow" Wheel Barrels/Lips in a chrome finish, designed for the modular ZeroRC wheel system, compatible with the RW00 series RWD chassis. 
 
Key Specifications & Features:
 
Modular Component: These are specifically the "lips" or "barrels" only, forming the main structure of the wheel. You must pair them with a compatible wheel face to create a complete wheel assembly. The "-6-4" designation indicates a narrow wheel frame/barrel, typically used for front tires or narrow rear setups.
Material: High-quality plastic or composite material with an electroplated chrome finish.
Quantity: Sold as a 4-pack, providing enough barrels for a complete set of four narrow wheels.
Compatibility: Designed for the ZeroRC RW00/SR RWD chassis and Mini-Z RWD platforms. They are not compatible with most AWD hubs