Hamilton Caliber H-51

The Hamilton caliber H-51 is a Swiss made mechanical bi-compax chronograph movement with 25 jewels and a frequency of 4 Hz (28,800 vph). This caliber does not have a date. Watches with this movement were introduced in March 2021.

In Hamilton’s own words:

“The H-51 is a mechanical chronograph movement that celebrates the fundamental principles of watchmaking. Featuring an extended 60-hour power reserve, this hand-wound caliber keeps and measures time with a combination of modern precision and vintage-inspired charm.” –Source

Base Caliber – ETA A05.291:

You will see most other watch sites state somewhat incorrectly that the H-51 is based on the ETA 7753. That is only part of the story here. The H-51 is actually essentially a Hamilton branded ETA calibre A05.291, which itself is based on the ETA 7753.

The 7753 is an automatic movement, but the A05.291 (and therefore the H-51) uses a similar framework, but without the automatic winding unit.

There is a cover plate used in place of where the automatic bridge would be, giving real estate for the laser engraved Hamilton logo and (sun rays?) design in the center.

On their Intra-Matic Chronograph H product page, Hamiltion states that the H-51 is exclusive to them”

“Feel the emotion at the heart of watchmaking with each wind of the Intra-Matic Chronograph H. Powered by our new, exclusive hand-wound chronograph movement the H-51 this is a timepiece with soul.” –Source

The H-51 may be exclusive to Hamilton with its custom branding and bi-compax layout, and while Hamilton and ETA are both owned by the Swatch Group conglomerate of watch brands, the A05.291 itself is not exclusive to Hamilton.

For example, Tissot also uses the A05.291 as a base movement for the PR516 Chronograph Mechanical – although the execution is different as a tri-compax chronograph with 24 jewels and Nivachoc anti-shock with no micro-regulator. The point is, it’s also an A05.291 base, the same number under the balance wheel of the H-51.

Interestingly, Tissot describes their use of the A05.291 like this:

“For the first time, Tissot incorporates the Valjoux A05.291 movement, specifically designed for the new PR516 Chronograph Mechanical.”

Swatch can’t seem to make up their minds about who exactly the A05.291 was made exclusively and specifically for.

H-51 VS H-51-Si:

There is another variant of the cal. H-51, which is the H-51-Si. The main difference here is that the Si version has an anti-magnetic silicon hairspring. All other specs appear to be the same.

In Hamilton’s own words:

“The H-51-Si is a mechanical chronograph movement featuring a state-of-the-art balance spring made from the anti-magnetic material silicon for enhanced resistance to extreme atmospheric conditions. With an extended 60-hour power reserve, this hand-wound caliber keeps and measures time via an iconic dial complete with start/stop and reset pushers. With no rotor and no date function, this interactive movement brings modern reliability and precision to signature, vintage-inspired design.” –Source

As of this article, the -Si version is found in the Hamilton Khaki Aviation Pilot Pioneer Mechanical Chrono.

On the same page, they also describe the upgraded balance spring as:

“Immune to magnetic fields, temperature fluctuations, oxidation, aging, shocks, and maintains shape stability.” -Source same as above

Additional Resources:

• More Hamilton watch movements