Automobil parts and automobiles companies are called auto ancillarys. Ancillary is used to describe something of secondary importance. one common use of the word is to describe an estate administration done in another done in addition to the primary administration in the state where the decedent died. Ancillary industries are those which manufacture parts and components to be used by larger industries. Eg- Companies like GE (ancillary) produce engines for the aircraft industry.