Parts of Rat Rod

Chassis
Frames from older cars or light trucks are preferred for the chassis, because they provide a sturdy base for subsequent alterations. Older cars in poor condition are often advertised as candidates for rat rod conversions. But in many cases the owner will design & build the frame them self.

Paint and Finish

Typical "rough" finish of Rat Rods.
Many Rat Rods appear unfinished with primer paint jobs being common. Other finishes may include “natural patina” (the original paint with rust and blemishes intact), a patchwork of original paint and primer, or bare metal with no finish at all in rusty or oiled varieties.With the thought that "It's only original once." Many rat rods also have free hand pinstriping done by the owners with a pinstriping brush. Contrary to tastes of many car builders, rust is often acceptable and appreciated by a Rat Rodder.

Interior
Interiors of rat rods vary from fully finished to a spartan, bare bones form. Mexican blankets and bomber seats form the basis of many rat rod interiors. Most are designed to be functional without many comforts although this will vary with the owner’s taste.

Drive train
Though a variety of engines may be used, the most common are to be found in a Rat Rod are Flathead V8's, early Chrysler Hemi engines, or more modern Small Block V8's from any manufacturer, especially Chevrolet. It is not uncommon to see straight-8s straight-6s, straight-4s, V6s or even diesel engines. These engines may exhibit varying displacements and modifications.
Most Rat Rods are rear wheel drive, with an open driveline. The rear-ends are typically passenger vehicle pieces, as are the transmissions. The Ford Banjo rear-end is popular, as is the "Quickchange" type as used in many early hot rods.

Suspension
A beam axle is commonly accepted as the only type of front suspension that will look right when exposed without fenders on a vehicle with open front suspension. Independent front suspension is discouraged, Most Rat Rods use a 1928-1948 Ford I beam axle with a transverse leaf spring. Although any solid axle is acceptable, the Ford axle is preferred due to the availability of spare parts.
Springs vary from transverse, parallel and coil setups in the front and rear. Parallel is not seen as frequently as the more common single-spring transverse setup, though both are used commonly. Coil springs are often deemed unsightly without fenders, but are still occasionally seen. Rat rods also will often have airbag suspension which allows the driver to raise and lower the car.

Criticism
Preservationists believe that modification of any rare surviving historical vehicle should be discouraged. In addition, traditional Hot Rodders criticize Rat Rods as mere imitations or anachronistic.

Origins
The December 1972 issue of Rod & Custom Magazine was dedicated to the beater, a low-budget alternative to the over-polished, slickly-painted, customized early car. The beater could easily be considered a progenitor of the rat rod. However, owners of these beaters often had a high-dollar machine sitting in their garage: no expensive upholstery, primered if painted at all, no chromed and polished Corvette/Jaguar rear ends.
As with many cultural terms, there are disputes over the origin of the term "rat rod". Some say it first appeared in an article written in Hot Rod Magazine by Gray Baskerville about cars that still sported a coat of primer. Some claim that the first rat rod was owned by artist Robert Williams who had a '32 Ford Roadster that was painted in primer. Hot Rod magazine has since verified this.[1]Although the term likely started out as derogatory or pejorative (and is still used in this way by many), members of the subcultures that build and enjoy these cars have adopted the term in a positive light.