[GeoffC]

Originally Posted by Mortis

Thats why the Robertson head screws are vastly superior 5 different sizes and all can be used upside down (screwed in to something over your head). I can't count the number of screws I've driven through 3 inch planks, couple hundred thousand at least!

"A Robertson, also known as a square, 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 to make inserting the tool easier. Robertson screws are used mainly in Canada (where they are very common), though they can be found elsewhere."

Is that one size only ?