Before ordering parts it is helpful to know the year, the make and the type of truck that you are working on.
The following descriptions will help you to determine the make and type of your truck.

Stepside / Flareside / Narrow Bed

These trucks are full size with large fenders on the outside of the bed, and the 'step' outside the bed as well. GM and Dodge refer to these trucks as 'Stepsides', while Ford calls them 'Flareside' trucks.

Chevrolet 1950 Stepside.

Dodge 1977 Stepside.

Ford 1941 Flareside.

Fleetside / Styleside / Wide bed

These full size trucks have straight sides and wheel tubs inside the bed. The GM name for these trucks is 'Fleetside' , while Ford calls them a 'Styleside'. Other names are 'Wideside' (GMC), 'Straight-side', etc.

Chevrolet 1959 Fleetside.

Ford 1966 Styleside.

GMC 1963 Wideside.

Cameo

This Chevy 55-58 series truck has the same size inner bed as a Stepside, but it has fiberglass outer bed side panels attached which makes the truck look like a later model Fleetside truck. It is not as common as the regular 55-58 series. The tailgate is different on this truck.

Chevrolet 1958 Cameo.

GMC 1956 Cameo.