2025

Apr.24, 2025

MinebeaMitsumi's 15 Miniature Ball Bearings Adopted for the World's First Mechanical Wrist-Metronome, Tempo Rubato

MinebeaMitsumi Inc. (head Office: Nagano Prefecture, Representative Director, Chairman & CEO: Yoshihisa Kainuma; hereinafter referred to as "MinebeaMitsumi") is pleased to announce that 15 of its miniature ball bearings, along with the world's smallest ball bearings,* have been adopted for the world's first mechanical wristwatch-style metronome, Tempo Rubato**, produced by Gaku Okada. This innovative wrist-metronome is now part of the collection at Musée International d'Horlogerie, Switzerland's international watch museum.

Tempo Rubato

Close-up Image of Tempo Rubato

While there have been mechanical pocket watch metronomes and quartz wrist-metronomes, Tempo Rubato is the world's first^** mechanical metronome designed in a wristwatch size, which applies the fundamental components of mechanical wristwatch, including wheels, springs, balance and escapement.

As movement-supporting components in the mechanical wrist-metronome, Tempo Rubato, all bearings used are manufactured by MinebeaMitsumi—instead of the traditional ruby ball bearings commonly employed in the watchmaking industry.

Of the 15 miniature ball bearings used in Tempo Rubato, 13 are MinebeaMitsumi's DDL-310 model (outer diameter: 3.0 mm, inner diameter: 1.0 mm, width: 1.0 mm), incorporated into key components such as the regulator, winding mechanism, pallet fork pivot, and BPM adjustment components. For instance, the regulator requires a miniature-sized yet robust bearing with the longest possible inner diameter, as force is applied directly through the bezel—demanding high load resistance. This specific requirement led to the selection of MinebeaMitsumi's DDL-310 bearing.

The remaining two, on the upper and lower pivot of the hands, are MinebeaMitsumi's world's smallest ball bearings (DDL-004, outer diameter: 1.5 mm, inner diameter: 0.5 mm, width: 0.65 mm). They are high-precision miniature ball bearing that serves as the pendulum's pivot, supporting the axis without lateral deviation, while remaining unaffected by the torque generated by the side-to-side motion of the hands.

* Minebea's Bearing with 1.5 mm in Outer Diameter achieved a GUINNESS WORLD RECORDS™ title for the Smallest Commercially Available Steel ball bearing

• ** According to Precision Watch Tokyo Co., Ltd.

Details of GAKU's Tempo Rubato

Tempo Rubato is a music term that refers to the practice of freely changing the tempo during a performance to match the atmosphere or feeling of the moment. In this work, the tempo (BPM) can be freely adjusted by rotating the bezel. In April 2025, it was added to the collection of the Swiss's largest watch museum, Musée International d'Horlogerie.

Functions

• Push button at the 8'o clock position: Starts and stops the metronome
• Bezel clockwise rotation: Increases BPM and winds the mainspring
• Bezel counterclockwise rotation: Decreases BPM (both directions have end stops)

How to Use

• Use the push button to start and stop the metronome, and rotate the bezel to adjust the BPM.
• The ideal way to adjust the BPM is to align it by rotating the bezel counterclockwise from a higher BPM to a lower BPM (This prevents misalignment with the click mechanism during winding).
• The BPM can be adjusted even while the metronome is working.

Specifications

Profile of Gaku Okada

About MinebeaMitsumi

MinebeaMitsumi is an INTEGRATED^** precision components manufacturer that engages in the development, manufacture, and sale of mechanical and electronic devices and components such as semiconductors, motors, and sensor with a focus on core technologies typical of ultra-precision machining. Our products include global market leading items such as miniature and small-sized ball bearings, which enable machines to rotate smoothly, for which we hold the highest share in the world^*, and 1 cell protection ICs for lithium ion batteries. Our ultra-precision technologies are used in a wide range of fields, supporting people's lives in unseen ways, including home electronics such as air conditioners, vacuum cleaners, dryers, and gaming equipment, IT devices such as smartphones and computers, automobiles, aerospace products, and medical equipment.

Website

* According to MinebeaMitsumi

• ** This term was adopted with the intended meaning "to be combined" rather than "to sum up," creating new value through synergy by combining all the resources of MinebeaMitsumi group.

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