A lead sled is a standard production automobile with a body heavily modified in particular ways ; especially, though not exclusively, a 1949, 1950, or 1951 model year Ford 'Shoebox' or Mercury Eight car. In the name, "lead" refers to the use of lead as a bodyfiller in early days, and "sled" refers to the lowering of the vehicle, giving these vehicles the appearance that they were "slip sliding" down the highway.