Step 5: Robertson® Drive
While not a true cruciform recessed drive (similar physical force principals apply to a square and a cruciform as shown in Step 7), it will be important to understand these as well. Note: Square Drive is not identical to Robertson.
In 1908, square drive screws were invented by Canadian Peter L. Robertson. Twenty-eight years before Henry Phillips patented his Phillips head screws. The Robertson screw is considered the "first recess-drive type fastener practical for production usage." The design became a North American standard.
Henry Ford used Robertson screws in the Model A car made by the Ford Motor Company (one of Robertson's first customers). The Model T used over seven hundred Robertson screws. Ford dropped these screws when Robertson refused to give him exclusive rights to its use. Robertson also refused to license other fastener manufacturers, so the design spread very slowly. Many recreational vehicles built in the 1950s use these screws. In Canada, most wood and electrical screws have Robertson recess heads.
Advantages and Disadvantages of Robertson Screws
A square recess drive allowed the screw to be placed on the driver prior to the screw being placed in position, so for the first time ever you could start a screw overhead or in a tight spot without an extra hand holding the screw onto the driver. A Robertson head on a screw is much better than a slot head because the screwdriver has great resistance to camout of the screw's head during installation and 4 possible positions to insert the driver. The Robertson drive design utilizes a "Morse-like" taper so the screw will stick to the bit even when held straight down. This taper allows the tool bit to insert deeper into the recess for more contact surface and thus less camout. To avoid problems make sure both screw and driver are of the matching type as there are many square drive drivers and screws around today that are not Robertson. See Square Drive (next topic). Robertson screwdrivers are available in 6 standard tip-sizes, none metric. Orange and orange are seldom used. The largest black is quite rare. Each identified usually by the handle color rather than by number.
Thanks Brian J. Cooley, Robertson Inc., Tools Division Product Line Manager for North America, for adding information on the 6th Robertson size and for pointing out ALL true Robertson Inc. power bits and insert bits are of the 2 piece variety, they have never produced one piece bits. (I've changed the reference picture as the original one was not not a true Robertson). An easy way for consumers to tell if any fasteners came from Robertson Inc. They use the ® following Robertson ® on all of the products manufactured.