With her characteristic "double bubble" roof was presented in 1955. It was built on the floor pan of the Fiat 600 and had 42 bhp available. The original model was also offered in a more luxurious variant for export (called "America", as it was almost strictly meant for the United States) and a stripped down model with lower, uncovered headlamps and smaller taillights for the domestic Italian market. The "America" also has a different layout around the rear license plate. The all-aluminium bodywork has Zagato's famous "double-bubble" design and Abarth's tuned derivazione engine with 43 CV (32 kW; 42 hp).

The 750 GT Bialbero model, a version with twin camshaft developing 57 bhp appeared at the 1958 Turin Auto Show. Along with various alterations to the bodywork it has the new twin-cam engine with 57 CV (42 kW; 56 hp) at 7000 rpm. A first series of 100 cars was sufficient for homologation in the GT Championship. 750 Bialbero-equipped Fiat-Abarth Zagato Record Monzas featured a lower roof with no bubbles and one single centered air scoop on the engine lid. "The Record Monza" was the most successful racing cars of all times, winning over 700 races worldwide, including both Sebring with the 750 cc Bialbero engine and Daytona under-1000 cc races in 1959.

By the time of the appearance of the Abarth Zagato Record Monza 750 Bialbero, the bodywork had been unified into a separate model with a rather large hump on the engine lid, made necessary by the taller twin-cam motor. There were then three distinct models: 750 "Double Bubble," 750 "Record Monza", and 750 "Sestrière."

The Sestrière had a single cam pushrod engine, and the majority were built with a steel body, a very small number of alloy cars, and there is one aluminium car known to exist today. The Sestriere had upright headlights, and two very large air intakes on the engine lid, much wider than a double bubble.

We had the chance to see many of these raging double bubble in various versions throughout the years ... check them out in our photo gallery