We slotted drivers into four groups: MODERATE—Less than 4,500 grams-centimeters squared ABOVE AVERAGE—4,500-4,900 HIGH—4,900-5,500 EXTREME—Higher than 5,500 More From the Hot List ...

they also were responsible for dissatisfaction with the slotted drive. Inventors wanted to do better. In 1908, Canadian Peter Robertson invented a square-head screw drive where the driver and the ...