Where another screw would have a straight line or a transverse shape, Robertson screws have a square socket. Also known as square or Scrulox screws, they are designed to make it easy to hold a square drill or screwdriver head in place when attaching. This makes them a little easier to work with alone.
Discovered by Canadian PL Robertson in 1908, Robertson screws are still more popular in that country to this day, although their use has expanded around the world, mainly for woodworking, construction and assembly of machines as switch terminals. The small taper used by Robertson was an improvement on an earlier square screw design patented by American Allan Cummings in 1