Robertson, also known as a square, or Scrulox screw drive has a square-shaped socket in the screw head and a square protrusion on the tool. Both the tool and the socket have a taper, which makes inserting the tool easier, and also tends to help keep the screw on the tool tip without the user needing to hold it there. (The taper's earliest reason for being was to make the manufacture of the screws practical using cold forming of the heads, but its other advantages helped popularize the drive.) Robertson screws are commonplace in Canada, though they have been used elsewhere, and have become much more common in other countries in recent decades. Robertson screwdrivers are easy to use one-handed, because the tapered socket tends to retain the screw, even if it is shaken. They also allow for the use of angled screw drivers and trim head screws. The socket-headed Robertson screws are self-centering, reduce cam out, stop a power tool when set, and can be removed if painted-over or old and rusty. In industry, they speed up production and reduce product damage. One of their first major industrial uses was the Ford Motor Company's Model A & Model T production. Henry Ford found them highly reliable and saved considerable production time, but he couldn't secure licensing for them in the United States, so he limited their use solely to his Canadian division. Robertson-head screwdrivers are available in a standard range of tip-sizes, from 1.77mm to 4.85mm.