NPR-RIKEN CORPORATION
Japanese automotive and industrial parts group formed by the 2023 merger of piston-ring makers Riken and Nippon Piston Ring.
Last updated September 27, 2026
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Overview
NPR-RIKEN CORPORATION (リケンNPR株式会社) is a Japanese corporate group headquartered in Chiyoda, Tokyo, created on 2 October 2023 as a joint holding company through the management integration of Riken Corporation and Nippon Piston Ring Co., Ltd. (NPR). Both predecessors were leading makers of piston rings and other automotive components, and had been competitors before the integration. The new company listed on the Tokyo Stock Exchange Prime Market on the same day it was established. The group's core business is automotive parts, especially piston rings, where it serves global automakers and contributes to the development of motorization worldwide. Its portfolio also spans marine and industrial products, piping products, metal injection molding (MIM) parts, thermal engineering, EMC (electromagnetic compatibility) business, and medical and disaster-emergency related products. After an organizational restructuring in April 2026, the company moved from a pure holding company to an operating holding company, taking over the sales, development, and corporate functions of its former subsidiaries Riken and Nippon Piston Ring. Manufacturing operations were consolidated into subsidiaries, including Riken NPR Niigata and Riken NPR Precision. The company operates through six business divisions: Piston Ring, Marine & Industrial, Precision Components, Material (casting), Piping Equipment, and Semiconductor & Electronics-related. It also engages in metal injection molding, surface treatment, functional resins, magnetic materials, and medical/disaster emergency products. The group has an extensive domestic and international network of subsidiaries and affiliates, with operations in Taiwan, Thailand, the United States, Indonesia, and other markets. NPR-RIKEN positions itself as supporting "the present and future of the Earth" by combining the experience and strengths of its predecessor companies to address environmental changes such as carbon neutrality and the electrification of the automotive industry. It pursues sustainability management and a business portfolio reform as part of its medium-term management plan.
History
The history of NPR-RIKEN CORPORATION is rooted in two separate Japanese companies that both specialized in piston rings: Riken Corporation and Nippon Piston Ring Co., Ltd. (NPR). Riken's origins trace back to 1926, when Dr. Keikichi Ebihara of the RIKEN (Institute of Physical and Chemical Research) Ohkoshi Laboratory invented a manufacturing method for piston rings that applied uniform pressure to cylinder walls, obtaining patents in multiple countries. In 1927, Rikagaku Kogyo Co., Ltd. was established to commercialize the invention, and it began manufacturing Japan's first practical piston rings. In 1932, a Kashiwazaki plant was built in Kashiwazaki, Niigata Prefecture. In 1934, the Kashiwazaki plant was separated to form Riken Piston Ring Co., Ltd., which after renaming, splitting, and merging led to the establishment of Riken Kogyo Co., Ltd. in 1941. After World War II, the company was reorganized and restarted in 1949 as Riken Kashiwazaki Piston Ring Industrial Co., Ltd. (renamed Riken Piston Ring Industrial Co., Ltd. in 1950) and Riken Kumagaya Cast Iron Co., Ltd. (renamed Riken Cast Iron Co., Ltd. in 1951). It listed on the Tokyo Stock Exchange in 1952. In 1953, it moved its head office to Nihonbashi, Chuo-ku, Tokyo, and merged Riken Cast Iron to form the Kumagaya plant. In 1967, it jointly developed oil seals and side seals for rotary engines with Toyo Kogyo (now Mazda). From the late 1960s, it expanded overseas, establishing Taiwan Riken Industrial Co., Ltd. in Taiwan in 1968, Siam Riken in Thailand in 1973, Riken of America in the United States in 1974, and P.T. Sri Riken Vigna Indonesia in Indonesia in 1975. NPR's origins trace back to 1912, when Tomokuni Suzuki, who had independently studied marine engine technology, opened Suzuki Works, beginning the design and manufacture of hot-bulb marine engines and rice milling machines. Recognizing the need for domestic piston ring production, he completed a prototype in 1931 and renamed the company Nippon Piston Ring Works. In 1934, it incorporated and opened a Kawaguchi plant in Kawaguchi, Saitama Prefecture. In 1939, it built a plant in Kumagaya, Saitama Prefecture for automotive and aircraft piston rings. In 1948, it began production of Koma-brand piping fittings. It listed on the Tokyo Stock Exchange in 1949. In 1960, it moved its head office to Uchisaiwaicho, Chiyoda-ku, Tokyo. Both companies grew as major suppliers of piston rings to the automotive and marine industries. In the 2020s, amid structural changes in the automotive industry including electrification, the two competitors decided to integrate. On 27 July 2022, Riken and Nippon Piston Ring announced a basic agreement to establish a joint holding company through a joint share transfer, originally planned for April 2023. Due to the Japan Fair Trade Commission's merger review, the schedule was postponed in November 2022. On 2 May 2023, the JFTC notified that it would not issue a cease-and-desist order. On 23 May 2023, the integration was formally decided, with share transfer ratios of 1.02 NPR-RIKEN shares per Nippon Piston Ring share and 2 NPR-RIKEN shares per Riken share. Both companies were delisted on 28 September 2023, and on 2 October 2023, NPR-RIKEN CORPORATION was established and listed on the Tokyo Stock Exchange Prime Market. After the integration, the company worked to unify production and R&D. In February 2024, through Riken, it made Shinwa Banesu Co., Ltd., a maker of heaters for semiconductor manufacturing equipment, a subsidiary. In February 2026, Siam NPR in Thailand absorbed Riken Sales and Trading (Thailand) and changed its name to NPR-RIKEN (Thailand). In April 2026, the company transitioned to an operating holding company with a divisional structure based on strategic business units, and its U.S. subsidiary Riken Corporation of America acquired Hastings Holding Corp., a U.S. piston ring maker, making it a subsidiary. Also in April 2026, the sales, development, and corporate functions of Riken and Nippon Piston Ring were transferred to NPR-RIKEN through a company split, and the manufacturing divisions were consolidated into subsidiaries renamed Riken NPR Niigata and Riken NPR Precision.
- 2026
February: Siam NPR in Thailand absorbs Riken Sales and Trading (Thailand) and changes name to NPR-RIKEN (Thailand).
- 2024
February: Shinwa Banesu Co., Ltd., a maker of semiconductor manufacturing equipment heaters, becomes a subsidiary through Riken.
- 2023
May 2: JFTC notifies it will not issue a cease-and-desist order.
- 2023
May 23: Integration formally decided; share transfer ratios announced.
- 2023
September 28: Riken and Nippon Piston Ring delisted.
- 2023
October 2: NPR-RIKEN CORPORATION established and listed on the Tokyo Stock Exchange Prime Market.
- 2022
July 27: Riken and Nippon Piston Ring announce basic agreement to integrate management through a joint holding company.
- 2022
November: Integration schedule postponed due to Japan Fair Trade Commission merger review.
- 1975
Riken establishes P.T. Sri Riken Vigna Indonesia in Indonesia.
- 1974
Riken establishes Riken of America in the United States.
Products and positioning
A global automotive parts group leveraging the combined experience of Riken and NPR to support carbon neutrality and next-generation mobility.
Piston rings
Automotive, marine, and industrial piston rings, the group's core product.
Camshafts
Cast iron camshafts and other material products.
Piping fittings
Koma-brand piping fittings for water, gas, and air conditioning.
Metal injection molded (MIM) parts
Precision metal injection molded components.
Thermal engineering equipment
Heaters for semiconductor manufacturing equipment and industrial furnaces.
EMC anechoic chambers
Electromagnetic compatibility testing facilities.
Medical and disaster emergency products
Products related to medical and disaster emergency applications.
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