2025
Jan.15, 2025
MINEBEA MITSUMI Inc.
MinebeaMitsumi's new miniature ball bearing adopted
for ŌTSUKA LŌTEC's watch "No.5 KAI"
-Japan's first mechanical watch with the satellite hour mechanism-
MinebeaMitsumi Inc. (head Office: Nagano Prefecture, Representative Director, Chairman & CEO: Yoshihisa Kainuma; hereinafter referred to as "MinebeaMitsumi") is pleased to announce that its newly designed miniature ball bearing, along with the world's smallest ball bearing*1 have been adopted for the mechanical watch "No.5 KAI" by the Japanese watch brand, ŌTSUKA LŌTEC.
The watch in the image indicates 5:45
(From left) MinebeaMitsumi's World's Smallest Ball Bearing and
new miniature ball bearing
ŌTSUKA LŌTEC, a Japanese watch brand, was established by Jiro Katayama, a recipient of the Contemporary Master Craftsman Award*2 and winner of the Grand Prix in the "Challenge Watch Prize" Category (for watches priced at 3,000 Swiss Francs or less) at the 2024 Le Grand Prix d'Horlogerie de Genève (GPHG), known as the Academy Awards of the watch world.
This newly announced model "No.5 KAI" is not only the first Japanese-made watch equipped with the satellite hour mechanism*3, but also the world's first mechanical watch with the satellite hour mechanism*4 that switches the "hour disk" by directly engaging with a pin and a bearing.
In mechanical watches, the "second disk" displays second numbers while providing a continuous view of the mechanism. The "No.5 KAI" employs MinebeaMitsumi's world's smallest ball bearing (outer diameter: 1.5 mm, inner diameter: 0.5 mm, width: 0.65 mm) at the 5 o'clock position of the "second disk," ensuring the smooth operation of the entire watch. On the other hand, the "hour disk" switches hour numbers through rotation. To use a ball bearing as a guide roller for the hour disk as it revolves, the ball bearing has to provide not only high rigidity but also has to be perfectly sized for watch applications. This type of bearing ensures the smooth and instantaneous switching of the "hour disk."
To meet the requirements for the guide roller of "hour disk," MinebeaMitsumi has newly designed a miniature ball bearing dedicated for the "No.5 KAI" model (outer diameter: 2.5 mm, inner diameter: 1.0 mm, width: 0.8 mm). This innovative ball bearing enabled the "No.5 KAI" to become the world's first watch equipped with the satellite hour mechanism that switches the "hour disk" by directly engaging with a pin and a bearing.
- *1 Minebea's Bearing with 1.5 mm in Outer Diameter achieved a GUINNESS WORLD RECORDS™ title for the Smallest Commercially Available Steel ball bearing
- *2 Contemporary Master Craftsman Award: "Award for Outstandingly Skilled Workers" given by the Ministry of Health, Labor and Welfare since 1967.
- *3 Satellite hours mechanism: A mechanism that features rotating numeral disks that that orbits like satellites, combined with fixed markers to indicate the time.
- *4 According to Precision Watch Tokyo Co., Ltd.
About MinebeaMitsumi's Miniature Ball Bearing
Ball bearing is MinebeaMitsumi's original business and starting point. The company's unwavering commitment to ultra-precision machinery technologies for over 70 years has been driving its ball bearing business. To achieve flexible control of machining dimensions at the nanometer scale and maintain machining precision, MinebeaMitsumi handles every aspects of production in-house, from cutting tools, to jigs, production equipment, environment preservation, and developing cutting-edge machining technologies.
Additionally, the manufacturing of the world's smallest ball bearing and the newly developed miniature ball bearing is carried out entirely by hand, from grinding to final assembly, by a selected group of skilled technicians within the company. This ultra-precision machining technology as well as a vertically integrated production system stand as one of MinebeaMitsumi's unique strengths, setting apart from its competitors.
Karuizawa Headquarters and Plant in Japan
The scene of hand-assembling ball bearings.
Details of MinebeaMitsumi's World's Smallest Ball Bearing (DDL-004)
| Size | Outer diameter: | 1.50 mm |
|---|---|---|
| Inner diameter: | 0.50 mm | |
| Width (thickness): | 0.65 mm | |
| Location of production | Japan (Karuizawa Plant) | |
Details of the Newly Designed Miniature Ball Bearing (DDL-008)
| Size | Outer diameter: | 2.50 mm |
|---|---|---|
| Inner diameter: | 1.00 mm | |
| Width (thickness): | 0.80 mm | |
| Location of production | Japan (Karuizawa Plant) | |
(From left) MinebeaMitsumi's World's Smallest Ball Bearing and
new miniature ball bearing (One scale on a ruler is 1mm)
Comparison between MinebeaMitsumi's world's smallest ball bearing, new miniature ball bearing and a matchstick
About ŌTSUKA LŌTEC's "No.5 KAI"
"No.5 KAI" is a satellite hour watch that inherits the design of the "No.5" model, a mechanical watch launched in 2012. In November 2024, it was added to the collection of the International Watch Museum (Musée International d'Horlogerie) in La Chaux-de-Fonds, Switzerland, the country's largest watch museum. Starting in February, the "No.5 KAI" will be showcased in a physical display in Harajuku. And in March, an online public raffle sale will launch, available exclusively in Japan.
| Functions | Satellite hours and minutes, Seconds disk |
|---|---|
| Winding | Automatic |
| Movement | MIYOTA 90S5 and In-house satellite hour module (Automatic, 25 jewels + 2 ball bearings, 28,800 vph (4 hz), Power Reserve: approximately 40 hours) |
| Case Diameter | 40.5mm |
| Case Thickness | 7.6mm (Including the crystal: 12.2 mm) |
| Case Material | Stainless steel (316L) |
| Case finish | Straight graining |
| Case-back | Display back |
| Water resistance | 3 ATM |
| Crystal | Sapphire crystal (Anti-reflection coating, Anti-fingerprint coating) |
| Strap Material | Calfskin |
| Lug widths | 22mm Made in Japan |
| Price | JPY 748,000 (tax included) 1year warranty |
About ŌTSUKA LŌTEC
"ŌTSUKA LŌTEC" is a Japanese watch brand founded in 2012 by Jiro Katayama, a contemporary master craftsman.
ŌTSUKA LŌTEC is the Japanese watch brand founded in 2012 by Jiro Katayama, a recipient of the Contemporary Master Craftsman Award. All of its watches are meticulously crafted in-house under the direction of Mr. Katayama. His career began as a car and product designer, but after winning a bench lathe through an online auction in 2008, he shifted to watchmaking and selling his watches in 2012. His creation "No.6" was awarded the Le Grand Prix d'Horlogerie de Genève 2024 in the "Challenge Watch Prize" category (for watches priced at 3,000 Swiss Francs or less).
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.
* This term was adopted with the intended meaning "to be combined" rather than "to sum up".
Create new value through synergy by combining all the resources of our group
- ** According to MinebeaMitsumi
| Media inquiries | Corporate Communications and Investor Relations Office Phone: +81-3-6758-6703 E-mail: koffice@minebeamitsumi.com |
|---|---|
| Sales inquiries of Bearings | Phone: +81-3-6758-6772 |
Product information, contact and other context are subject to change without prior notice.
