(EN) Canadian Inventions – The Robertson Screwdriver System (Peter Robertson), su Deeth Williams Wall, 30 maggio 2012. URL consultato il 21 marzo 2019.
«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.»
