| Brand: | Blancpain, Frédéric Piguet | 
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| Family: |
Unknown
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| Height: | 1.73 mm | ||
| Jewels: | 18 | ||
| Reserve: | 40 hours | ||
| Frequency: | 21,600 A/h | ||
| Winding: | Hand winding | ||
| Diameter: | 20.40 mm (9 ligne) | ||
| Complications: | |||
| Hands: | Central Hour Hand, Central Minute Hand | ||
| Distinguishing Technical Characteristics | |||||||||||
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 Ultra-Thin Hand-Winding  Hand-Winding  Counter-Clockwise Balance Cock |
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| Production: 1925 – Current | |||||||||||
| 1910s | 1920s | 1930s | 1940s | 1950s | 1960s | 1970s | 1980s | 1990s | 2000s | 2010s | 2020s |
F. Piguet Cal. 21 (also known as Piguet 21 and Blancpain 21) is an ultra-thin and compact hand-winding movement from Frédéric Piguet. It measures 20.40 mm in diameter (9 ligne) and just 1.73 mm thick. It remained the thinnest watch movement made for two decades after its 1925 introduction and remains one of the thinnest movements ever.
Blancpain takes credit for the design of Cal. 21, dating the start to 1911. But the company notes that they did not use the movement until “fifteen years later.” In 2003 they have referred to watches using this movement as the “Villeret Ultra-Slim with Hand-Wound Movement,” Ref. 0021.
It uses a flat hairspring for compactness. It originally used Lubrifix 66 to mount the balance wheel, later switched to Kif Duofix and Kif Ultraflex after 1985. Unusually for a compact F. Piguet movement, the balance cock is mounted counter-clockwise when viewed from the rear. The balance originally oscillated at 18,000 A/h but was updated to 21,600 A/h in recent decades. Power reserve is usually quoted as 40 or 42 hours.
The similar Cal. FP 21P is a skeletonized version.
Cal. FP 21 is used by many companies, notably Blancpain which would ultimately absorb Frédéric Piguet as Manufacture Blancpain in 2010. Patek Philippe used this movement as the basis for their Cal. PP 175 and Cal. PP 177, both using a Gyromax balance.
- Blancpain Cal. 21
- Cartier Cal. 21
- Certina Cal. 20-10
- Longines Cal. 310
- Omega Cal. 700
- Zenith Cal. 53.5
