Parts are used to build vessels in-game via the Vehicle Assembly Building. Parts are categorized by function and size. In Exploration Mode parts are unlocked for use by researching them using Science, whereas as parts are immediately available for use in Sandbox Mode.
Command modules
Pods
Probes
Cockpits
Rovers
Fuel tanks
Methalox
Methane
Monopropellant
Xenon
Engines
Methalox
Methane
Solid Fuel Boosters
Monopropellant
Xenon
Structures
Struts
Clamps
Engine Mounts
Adapters
Beams
Body
Panels
Hubs
Trusses
Truss Adapters
Truss Resizers
Tubes
Couplings
Stack Decouplers
Stack Separators
Stack Radial Decouplers
Stack Docking Ports
Payloads
Fairings
Cargo Bays
Crew Cabins
Trusses
Aerodynamics
Nose Cones
Air Intakes
Wings
Stabilizers
Control Surfaces
Tails
Ground
Landing Legs
Landing Gear
Wheels
Thermal
Heat Shield
Electrical
Batteries
Solar Panels
Generators
Communication
Antenna
Utility
Parachutes
RCS
Stabilizers
Lights
Ladders
Science
Science Experiments