One of the things that made Henry Ford's assembly line a reality was the interchangeability of car parts. Close to 14,000 parts make up the average vehicle we drive today. Most people, even the least mechanically minded among us, can name standard auto parts like brakes, windshield wipers, tires, and steering wheels. When describing other vehicles, they may be able to name other parts that are not normally found on passenger cars. Truck parts include bed liners and mud flaps. Other equipment that allows for hauling trailers like duallies, or that allows off-road usage in uneven terrain are another popular category of truck parts. Suspensions that raise the truck high above traffic, or lower it so much that it scrapes against tall speed bumps, can also be purchased in the aftermarket for owners who wish to customize their vehicles. Performance car parts are another specialized area. Performance and luxury cars are generally the first to introduce new technologies to the automotive consumer. This is where now-standard auto parts like disc brakes, heating and air conditioning systems for passenger comfort, glass fiber resin car panels, and on-board computers that continuously monitor engine variables to ensure proper fuel mixing and timing first made their debuts. The most common place for customers to get replacement car parts to fix their own automobiles are the giant chain stores like Checker and Auto Zone, a mass marketer like Walmart or Sears, or from a dealership that sells their make of vehicle. These three sources account for the majority of replacement car part sales. True devotees, however, scour the glossy catalogs and websites dedicated to their cream puffs, whether they are 1950's Chryslers, Ford trucks from the 1960's, or exotic sports cars. These catalogs and sites have all of the usual replacement car parts, but they are sometimes the only place where a hobbyist can find that door panel only found on the 1978 model, or an exact replica of the passenger-side seat to replace one that has gotten ratty over time, usually at a price that would make the average driver reconsider their purchase. They also feature other auto parts that aren't standard, generally trim pieces or products that supposedly enhance engine performance, so that customizers can create their own versions of what they think the vehicle should have looked like when it rolled off the assembly line.