Bristol Wrench
A Bristol wrench is a fastener driving tool used on Bristol spline drive fasteners. The Bristol design was created by the Bristol Wrench Company of Spokane, Oregon in the United States and was in use no later than the beginning of the 1950's.
The fastening end of the tool resembles a 4 or 6 toothed gear and mates to a similar hole in the fastener.
According to the company, the fasteners are of superior design because almost all of the turning force is applied at right angles to the fastener axis. The company also states that the fasteners are slow to wear out due to repeated manipulations.
Bristol spline fasteners are uncommon but were sometimes used, for instance, in Cold War era American military electronics.