Allen Head socket
There was a Mr. Allen and an Allen Manufacturing Company in Hartford, CT that promotes the Hex bolt and screw heads and the wrenches to turn them. The female bolt and screw head existed for many years before this company, but they popularized the tool and the name. The Allen Head requires less space (diameter) and can be used in recessed areas. The tolerances are tighter than normal bolts as well. This is more importance in places where weight and limited access space are the norm – In plane and aviation applications