Car parts and hoverboards on a plane
Identify the exact component before packing. At US checkpoints, a clean car part, a detached airbag and a battery-powered hoverboard have different baggage rules. The airline may also limit the size or weight of an otherwise permitted part.
Car parts without fuel
TSA allows car parts in carry-on and checked baggage only when they have no fuel or traces of fuel. A checked engine part must be in its original box and free of gasoline and oil. Protect exposed edges, and check that the part fits the airline's baggage allowance. Do not use this rule for an attached battery or a part with residual fuel. TSA: car parts; FAA: fuels.
Detached vehicle airbags
TSA lists a vehicle airbag as prohibited in both carry-on and checked baggage. Do not place a loose module in a suitcase with other car parts. If it must travel by air, ask a dangerous-goods shipper about cargo classification and packaging. TSA: vehicle airbags.
Recreational hoverboards
Ask the airline whether it accepts your hoverboard before bringing it to a US airport. Check the battery label: FAA requires airline approval above 100 Wh and prohibits a recreational board above 160 Wh in either bag. An accepted board must be protected from accidental activation, battery damage and short circuit. A device used as a disability mobility aid has a separate FAA entry. FAA: portable recreational vehicles.