By 1967, Fiat was leading the European market, and its 50th anniversary was coming up. For the occasion, a new series was developed in Turin with more innovative characteristics than earlier models. The new series would be based on the Diamante series, and the name chosen was "Nastro d'Oro" or "Gold Ribbon", marking the "Golden Anniversary" of Fiat's "marriage to the land".

The appearance was a strong evolution of the Diamant series, again penned by Pinninfarina, with the longitudinal ribs of the engine cover now more predominant, and running though to the nose conferring lightness and movement. The colors were slightly changed as well, with a lighter orange for the bodypart, and blue for the mechanical parts, which gave the impression of a dynamic and modern machine. 

The new series wasn't only a styling exercise though. The series introduced new upgraded engines, all now with direct injection and rotary injection pumps, and all but the smallest reverting to a stressed crankcase design. Improved driving ergonomics, a number of new safety features including a lock preventing starting the engine while in gear, new 12 volt electrical system, upgraded gearboxes with synchronizers, and the control-matic three-point hitch now standard on all models, are just a few of the technical features to mention.

Some sources tell, that all models at launch had the option of a Frutteto, Vigneto and Granluce variant, though this has been difficult to confirm.

The first models of the "Nastro d'Oro series"/"Gold Ribbon series", were put into production in 1968.

The 600 was introduced three years later, and only lastet from 1971 to 1973. The weak front axels on DT versions were upgraded to a heavier version in 1972, changing length and topspeed slightly.
As Fiat realized the performance difference of the 600 and 550 models were neglegeble, Fiat tuned the engine of the 600, resulting in the 640 model.
From 1973 till 1980, the 640 sales would dominate the Gold Ribbon series, with the officiel figure of 110.000 manufactured during its production run. Though that isn't the final number, as 640 is still manufactured to this day in Pakistan (including the 480), at a current rate of 25.000 units per year.
The 640 is probably the most widely distributed model in Fiat's history.
The 650, though part of the same model and horsepower category as the other 600's, was a different beast to the 600 and 640. Introduced in 1968, together with its true sibling the 750, the tractor was engined and manufactured by OM.

The 650 together with the 750 and 850, would be the last tractor sold under the OM brand, with the OM company being merged into the Fiat group in 1975, including their truck and bus division.
1975 would also be the last year for the 650, 750 and 850/850S, being replaced by the first 80-series models 780 and 880.
But until 1975, the 650 was sold in Italy under the OM brand, while on the international market, it and all the other 600-models, were sold under the Fiat brand. Except from France, were all models were still sold under the Someca brand, and from 1981 to 1984, when the 640 was sold in North America under the Hesston brand.

All models used a stressed chassis design, with the engines cast-iron crankcase being part of the tractors backbone. 

The 600's and 640's gearbox was an eight forward and two reverse, with the four highest gears synchronized, while the 650's gearbox was the old seven forward and two reverse, with no synchronizers. PTO and locking differential on the rear axle were standard on all model. The models was also offered with draft control / "Control-Matic".

The 600 and 640 adopted the 8045.02 engine. A four cylinder version of the 300's watercooled, direct injected diesel, with a displacement of 3.456cc, developing 60/64 hp at 2.400 rpm and
220/219 nm at 1.400/1.375 rpm.
The 650 used OM's own large three cylinder watercooled, direct injected diesel engine, with a displacement of 3.701cc, developing 65 hp at 2.200 rpm and 239 nm at 1.300 rpm, later 70 hp and 275 nm as the 650 Special.

The Gold Ribbon Series tractors enjoyed even greater success than its predecessor, being recognized for their new design, engines and features.
In 1968 alone, when the European market was contracting, Fiat produced a total of almost 60.000 tractors, 42.000 of which in Modena alone, 5.000 more than the previous year. That year also saw the production of the 500.000th Fiat tractor since 1918.