The sixth-generation Ford F-Series was introduced in 1973. This version, known as the Dentside to enthusiasts of the F-series, continued to be built on the 1965 fourth generation's revised platform but with significant restyling modernization and refinements. Front disc brakes increased cabin dimensions and comfort features, full double wall bed construction, increased use of galvanized steel were notable improvements over the previous generation. In 1975, the F-150 was introduced between the F-100 and the F-250 to avoid certain emission control restrictions. The F-350 was also continued on from the previous generation. A Crewcab or 4-door was available on the F-250 and F-350 platforms. A Supercab (2-door extended cab) became available on the F-250 platform to compete with Dodge's offering. Styleside and Flareside beds were available in either 6 1/2 or 8 foot bed configurations. The FE engine series was discontinued in 1976 after a nearly 20-year run, replaced by the more modern 335 & 385 series engines. A four-speed manual, three-on-the-tree manual, or a three-speed Cruise-O-Matic automatic transmission were options. All series featured Ford's Twin I Beam front suspension. For 1978, square headlights replaced the previous models' round ones on higher trim package models, such as Lariat and Ranger, and in 1979 became standard equipment. Also, for 1978, the Ford Bronco was redesigned into a variant of the F-series pickup. 1979 was the last year that the 460 engine was available in a half-ton truck. 1979 would also be the last year for Sixth Generation production, with the Seventh Generation F-Series replacing it.