Fenway Partners, Inc. bought the Bell Sports Crop from an investor group including GarMark Partners, L.P., Wachovia Investors, Inc. and Chartwell Investors,.
Fenway purchased Riddell in June 2003.
The combined company, which will produce more than 8 million helmets annually, will have projected 2004 revenues of more than $300m.
Together, Bell and Riddell will have the "world's largest research and development effort focused on head protection," said a statement from Fenway.
The combined company's management team will be led by Bill Fry, president and CEO of Bell.
Bell's Giro brand is a key sponsor of Lance Armstrong and Bell also sponsors BMX icon Dave Mirra.
Mark Genender, a managing director of Fenway Partners said:
"This strategic transaction reflects the Fenway value-creating model at work. We are bringing together a world class brand portfolio and two superb management teams who are fully capable of delivering on several identified growth opportunities. This combination will lead to accelerated new product introductions, as well as future acquisitions that will leverage the R&D capabilities of the combined company and increase market penetration."
The merger also reunites Bell and Riddell, which were once part of the same holding company until 1984, when investors sold the two companies in separate transactions.
Bell also owns the accessory brands Blackburn, VistaLite, CoPilot and Savasa.