Automotive Usage

Originally, the lead sled referred to extensively repaired/modified cars due to the use of lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 as body filler and was, for the most part, an insult.

Since the introduction of artificial fillers (such as Bondo

Bondo (putty)

Bondo is a brand of two-part putty manufactured by 3M. Originally used mainly for automobile body repair, Bondo has been widely used by carpenters to repair wood. The Bondo brand of filler or putty is composed of a polyester resin that, when mixed with a hardener or catalyst, turns into a putty...

), the term has come to mean a post-war, large (full size) American car

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 of the 1950s.

A lead sled tends to have all extra side moldings shaved off and filled with the suspension lowered. Lead sleds are built for style, not speed. Some common lead sleds are the 1949 Mercury, 1949 Ford and the 1959 Cadillac.

Other Usages

Aircraft nicknames - It has also been used as a nickname for a variety of US military aircraft, including the F3H Demon

F3H Demon

The McDonnell F3H Demon was a subsonic swept-wing United States Navy carrier-based jet fighter aircraft. After severe problems with Westinghouse J40 engine that was ultimately abandoned, the successor to the McDonnell F2H Banshee served starting in 1956 redesigned with the J71 engine...

, F-84 Thunderjet

F-84 Thunderjet

The Republic F-84 Thunderjet was an American turbojet fighter-bomber aircraft. Originating as a 1944 United States Army Air Forces proposal for a "day fighter", the F-84 flew in 1946...

, F-105 Thunderchief

F-105 Thunderchief

The Republic F-105 Thunderchief, was a supersonic fighter-bomber used by the United States Air Force. The Mach 2 capable F-105 conducted the majority of strike bombing missions during the early years of the Vietnam War; it has the dubious distinction of being the only US aircraft to have been...

, and SR-71 Blackbird

SR-71 Blackbird

The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft. It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works. Clarence "Kelly" Johnson was responsible for many of the...

.