Italian jewellery company Bulgari has reclaimed the record for making the world's thinnest mechanical watch with the release of its Octo Finissimo Ultra Cosc, which has a thickness of just 1.7 millimetres.

It beat the previous record holder, Richard Mille's RM UP-01 Ferrari, by just 0.05 millimetres – about the breadth of a human hair.

The design is an evolution of Bulgari's Octo Finissimo Ultra, which held the record for four months in 2022 before the release of Ferrari's collaboration with watchmaker Richard Mille.

"The Octo Finissimo is a vast playground of innovation and design — and a source of unprecedented challenges — for Bulgari's R&D department," said the director of Bulgari's watchmaking division Antoine Pin.

All 170 components that make up the movement of the Octo Finissimo Ultra Cosc are fixed directly onto the back of the watch's case rather than onto a separate mainplate, just like in its predecessor.

To protect the mechanism in lieu of this additional layer, the case back is made of tungsten carbide – an ultra-durable metal alloy – while the front of the case and the matching strap are made of sandblasted titanium.

The new thinness was achieved by "optimising" the sapphire crystal front, according to Bulgari.

"Through patient, meticulous incremental steps, the engineers were able to shave off that critical tenth of a millimetre," the company said.

The final design is 1.7 millimetres thick or about the width of a five-pence coin.

The Octo Finissimo Ultra Cosc also presents an advance in terms of accuracy.

It is the thinnest watch to ever receive the chronometer mark by Switzerland's independent Contrôle Officiel Suisse des Chronomètres (COSC), which requires a timepiece to lose no more than four seconds and gain no more than six seconds a day.

The watch will be produced in a limited edition of 20, with a QR code on the back linking to an online product manual specific to the individual watch.

Each will also come with a case that will automatically set and wind the watch at the push of a button.

The release marks Bulgari's ninth world record for the thinness of its watches, as it is locked in a race with watchmakers including Richard Mille, Audemars Piguet and Piaget.

Other recent releases aimed at pushing traditional watch design include Frank Gehry's transparent Louis Vuitton timepiece and Formafantasma's Rado watch, which was designed to have a sense of secrecy.