Mutual insurers that insure factories and other business establishments and attempt to achieve favorable underwriting results through loss prevention techniques.

A group of direct-writing mutual insurance companies, independently owned and operated, which underwrite highly protected risks of substantial value on a reciprocal reinsurance basis. The central organization in New England maintains extensive fire laboratory facilities and provides its members with engineering services.

Member insurers of the Factory Mutual System, which is a group of mutual coinsurers formed to provide member insurers with insurance and engineering services.