another change, the model nomenclature of the F-Series was expanded to three numbers; this remains in use in the present day. The half-ton F-1 became the F-100 (partially influenced by the North American F-100 Super Sabre); the F-2 and F-3 were combined into the -ton F-250, while the F-4 became the one-ton F-350. Conventional F-Series trucks were F-500 to F-900; COE chassis were renamed C-Series trucks. While the cabs, doors, radiator support, inner fenders, and hoods are the same from 1953 to 1956 F-100 and F-250s (the fenders varied on F-250, F-350, and F-500, and long boxes were only available on the F-250), in 1956, the cab underwent a major revision. Centered around a wraparound windshield, the cab was given new doors, a redesigned dashboard, and an (optional) panoramic rear window. In line with Ford cars, the 1956 F-Series offered seat belts as an option. Third generation (1957–1960) Introduced in 1957, the third generation F-Series was a significant modernization and redesign. Front fenders became integrated into the body, and the new Styleside bed continued the smooth lines to the rear of the pickup. The cab-over F-Series was discontinued, having been replaced by the tilt-cab C-Series. In 1959, Ford began in-house production of four-wheel drive pickups. Fourth generation (1961–1966) Ford introduced a dramatically new style of pickup in 1961 with the fourth-generation F-Series. Longer and lower than its predecessors, these trucks had increased dimensions and new engine and gearbox choices. Additionally, the 1961–1963 models offered an optional unibody design with the cab and bed integrated. The traditional separate cab/bed was offered concurrently. The unibody proved unpopular, and Ford discontinued the option after the 1963 model year. In 1965, the F-Series was given a significant midcycle redesign. A completely new platform, including the "Twin I-Beam" front suspension, was introduced, and continued to be used until 1996 on the F-150, and still is currently on the F-250 and F-350 4x2. Additionally, the Ranger name made its first appearance in 1965 on a Ford pickup; previously, the Ranger denoted a base model of the Edsel, but starting in 1965, it was used to denote a high-level styling package for F-Series pickups. Fifth generation (1967–1972) Introduced in 1967, the fifth-generation F-series pickup was built on the same platform as the 1965 revision of the fourth generation. Dimensions were increased, engine options were expanded, and plusher trim levels became available during the fifth generation's production run.