Most race cars where the car builder cares about what he is doing use the AN system of hardware whereever possible. The AN ("Army-Navy") system was introduced going into WWII to provide a unified hardware system for aircraft assembly. The system includes nuts, bolts, and other fasteners as well as plumbing.
Shortly after WWII, George Bignotti (famous Indy car builder) found the surplus bins at Earl's in Gardena, California and started plumbing his cars with leftovers from the aerospace industry. The practice quickly spread throughout high end racing.
When MacNamara took over the DoD, one of the things he did was end cost-plus contracts, which as a side effect mostly killed the surplus industry. Aeroquip, the principal manufacturer of the AN plumbing fittings, declined to sell to Earl's, and so Earl designed his own hose ends and fittings and went into the manufacturing business.
Aeroquip eventually realized the error of their ways, and started selling to the performance automotive industry, but Earl's is still in business, and selling top notch fittings. A number of other manufacturers exist as well.