Analysis of information sources in references of the Wikipedia article "Impact driver" in English language version.
Millions of craft workers are thankful to Canadian Peter Robertson for inventing the square-head screw that bears his name. The Robertson screw represented a significant advance in the history of fasteners for two practical reasons: it is self-centering (that is, the screw is almost impossible to be driven off-centre because of the indented squared notch into which the screwdriver fits snugly) and the screw can be driven with only one hand.
