The first full-size prototype mock-up of the of the IH 50 series tractor design, code named TR4, built with the modified 86 series cab and wooden hood. Work on the new 50 series began in the mid-1970s. Three different variants were proposed in this early styling and design concept. The TR2, TR3, and TR4. The TR4 became the 50 series models, the TR3 became the 30 series, and the TR2 was never produced.