Robertson screw

Although most Canadian are familiar with good old Robertson's fastener for umpteen years, his name is not so well known outside of Canada. They are referred as Square drive in the US. P.L. Robertson was a Canadian inventor who was one of the first to solve successfully the major drawback of the common slot screw fastener; its annoying tendency to cam out and strip the head and damages the surrounding surfaces."
rovertson patent
Its invention, the Robertson square drive fastener, was simple to manufacture, requiring only two blows from the stamping head to shape the head and form the tapered recess for the driver. Original patent drawing 1909
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