Original Engine Management 4057 Distributor Cap Distributor caps are manufactured to match O.E. form, fit and function. They offer the following high-performance features: *Polypropylene, PBT, or Thermoset molding material for maximum dielectric strength and resistance to carbon-tracking Brass, aluminum, stainless, or tin-plated terminals and inserts for superior conductivity. Arc-resistant dielectric material Brass or aluminum insert material Internal resistor where required