The Small Chassis is the frame used to facilitate vehicle modules, being the smallest with 2 applicable slots. Facepunch added the modular vehicles in the Modular Vehicle Component Update on the 3rd of July, 2020.
Chassis types are spawnable in-game by RUST Admins using the F1 console and
entity.spawn command, but are not available for research or crafting by players.
Most naturally spawning chassis types in RUST are accompanied by a module type already included. Module types may be switched out once the chassis is placed on a powered Modular Car Lift.
For more information on modular vehicles, read our RUST Modular Cars Guide.