It depends on the rack family and what the base product includes. A headache-rack system may need vehicle-specific mounting brackets, side or rear bars, tonneau adapters, or accessory holders. A truck bed rack may use crossbars, load stops, tie-downs, track or tonneau adapters, or other mounting hardware. A van roof/ladder rack may need a vehicle-specific mount kit, cross members, ladder mechanisms, conduit carriers, or load-assist components. Buy accessories only after confirming they are designed for the exact rack system and vehicle application.