Robertson screw - Printable version

Generically known as square drive, a fastener distinguished by the square recess in its head. When using a powered screwdriver, the square drive is less prone to cam out or stripping out than the Phillips head.

Robertson Inc. - Standard Products

From http://www.robertsonscrew.com/index.html:

In 1908, P. L. Robertson began to manufacture a square recess impression in the head of a screw in Milton, Ontario, Canada. At that time, it was a revolutionary change in the fastener industry. The first patent was issued in 1909 and the last patent expired 55 years later in 1964. For his invention, P.L. Robertson screws and screwdrivers carry his name to this day.

Robertson screw Printable version