How it began
P. L. Robertson worked as a traveling salesman for a Philadelphia tool company. While he was demonstrating a tool, his straight-bladed screwdriver slipped out of the slot and cut his hand. That led him to design a screw with a square socket in the head that would slip less. He set up his company in Hamilton, Ontario, in 1907 and moved it the next year to Milton, Ontario, after the town offered a loan of 10,000 dollars for a factory. The Canadian patent is dated 1909.
Before it existed
Screws had a single straight slot, from which a driver slipped easily. A square-socket drive had been patented in 1875 by Allan Cummings, but it was never a commercial success, because the design was difficult to manufacture. Robertson's contribution was a way to make the square recess cheaply and in quantity.
How it works
The head has a square recess and the driver has a matching square tip, so the tool seats in the screw and tends not to slip. Robertson formed the socket by cold forming, pressing the shape into the head. It is that efficient manufacturing method that made the idea a commercial success. The screw can be driven with one hand and is easy to remove even after weathering.
Who pushed back
One of Robertson's first customers was the Fisher Body company, which made car bodies for Ford and used over 700 Robertson screws in each Model T. Henry Ford found the screw saved about two hours of work per car and sought an exclusive license to use and make it in the United States. Robertson turned him down, judging it not in his interest. Ford soon found that Henry F. Phillips had another socket screw and no such reservations.
Where it stands today
The Robertson screw is most popular in Canada. It is also used widely in boat building, because it tends not to slip and damage the material around it. The Canadian Encyclopedia has called the Robertson driver the biggest little invention of the 20th century so far.
