The Patek Philippe caliber 28-255 is one of the most important automatic movements in the brand’s history. Introduced in the 1970s, it is best known for powering the very first Patek Philippe Nautilus, the Ref. 3700/1, designed by Gérald Genta. This ultra-thin automatic movement, based on a collaborative project between top-tier Swiss brands, became a cornerstone in luxury sports watch evolution.

Overview of the Caliber 28-255

Launched in 1976, the caliber 28-255 was Patek Philippe’s version of the Jaeger-LeCoultre 920—a celebrated ultra-thin automatic movement originally developed in 1967. Notably, Patek Philippe, Audemars Piguet, and Vacheron Constantin were the only manufacturers authorized to use it, each with their own refinements. The 28-255 featured Patek’s enhancements in finishing, regulation, and assembly, making it arguably the most refined version of this movement.

The “28” refers to the diameter in millimeters (28mm), and “255” designates the movement series. Its ultra-slim height of just 3.05 mm enabled a thin, elegant case profile without sacrificing automatic functionality—perfect for luxury steel sports watches like the Nautilus.

Technical Characteristics

Despite its slender design, the 28-255 is mechanically sophisticated and remarkably robust. Its micro-rotor-like construction balances thinness with efficient winding.

Key specs:

• Type: Automatic winding with full rotor

• Diameter: 28.0 mm

• Height: 3.05 mm (ultra-thin profile)

• Frequency: 19,800 vibrations per hour (2.75 Hz)

• Power reserve: Around 40 hours

• Jewels: 36, supporting smooth rotation of the rotor and gear train

• Rotor: 21K gold, mounted on ball bearings for increased durability

• Finishing: Geneva stripes, anglage, polished screws, and perlage—meeting Patek Philippe’s highest decorative standards

The movement uses a free-sprung Gyromax balance for precise timekeeping and better resistance to shock and positional error.

Iconic Application: The Nautilus Ref. 3700/1

The most famous watch powered by the 28-255 is the Patek Philippe Nautilus Ref. 3700/1. Introduced in 1976, it marked Patek Philippe’s entry into the luxury sports watch category and set the tone for high-end steel watches. The ultra-slim case was made possible specifically by the thin profile of the 28-255.

Nicknamed the “Jumbo” due to its large 42mm case (huge for its time), the 3700/1 housed the 28-255 without adding bulk, helping maintain the elegance expected of a Patek Philippe timepiece.

Other high-end references used this movement as well, although the 3700 remains the most iconic.

Significance and Collectibility

The 28-255 is no longer in production, which only adds to its allure. Today, it is regarded as one of the most historically and mechanically important calibers from the 1970s. It’s especially significant for being part of the elite club of movements shared only among the “Holy Trinity” of Swiss watchmaking—Patek Philippe, Audemars Piguet, and Vacheron Constantin.

Collectors prize watches with this caliber not only for their aesthetics but for the movement itself. It’s rare to find such a thin automatic movement with full rotor construction and such beautiful finishing.

Maintenance Considerations

Servicing the 28-255 requires great care. Due to its thin profile and complex winding system, it's best handled by specialists familiar with vintage Patek Philippe calibers. Parts are rare, and improper servicing can affect performance or long-term value.

With proper maintenance, the 28-255 remains a reliable and beautifully smooth-operating movement.

Conclusion

The Patek Philippe caliber 28-255 is a horological icon. It blends ultra-thin engineering with automatic convenience and top-tier finishing. Its presence in the original Nautilus Ref. 3700/1 cements its legacy, while its rarity and elegance continue to fascinate collectors. For those who value form, function, and historic importance, the 28-255 is a movement that represents a pinnacle moment in watchmaking.