A Robertson, also known as a square or Scrulox screw drive is specified as ANSI Type III Square Center and has a square-shaped socket in the screw head and a square protrusion on the tool. Both the tool and the socket have a slight taper. Originally to make the manufacture of the screws practical using cold forming of the heads, this taper provides two other advantages which have served to popularize the drive: it makes inserting the tool easier, and tends to help keep the screw on the tool tip without the user needing to hold it there. Robertson screws are commonplace in Canada, though they have been used elsewhere and have become much more common in other countries in recent decades. As patents expired and awareness of their advantages spread, Robertson fasteners have become popular in woodworking and in general construction. Combination Robertson/Phillips drives are often used in the electrical trade, particularly in device & breaker terminals, as well as clamp connectors.