Sorry but that's factually incorrect, neither the PH or PZ drive systems have anything to do with Henry Ford. In fact Henry Ford was an opponent of the Phillips (PH) system, resisting its use on his production lines for nearly a decade. It was another Henry and his company that we must thank for the worlds most popular drive system and for the improvement spin-offs Posidriv (PZ), Superdriv and Mortorq.
Born in Portland, Oregon, Henry F. Phillips purchased the rights to a socket screw in the 1920s and redesigned the screw with a cruciform recess. The significance of his original design, the “crosshead” or early Phillips screw lies in its self-centring property. Unlike a traditional slot screw which required a person to simultaneously centre the screw in its hole, steady the screwdriver in the slot and then use the screwdriver to turn the screw, the Phillips screw’s cruciform head sat firmly on the screwdriver with no need to centre the screw in the hole.
Henry F. Phillips saw that there was need on the blossoming production lines of American automobile industry for some type of torque limiting driver or fastener system. He purposely re-designed his cruciform screw drive to cam out when the screw stalled, to prevent the fastener damaging the work or the head, instead damaging the driver. Damage on the production lines was caused by the relative difficulty in building torque limiting into the early drivers. Phillips patented this invention, an improved version of a deep socket with a cruciform, today known as the Phillips Screw.
Over the next few years, Phillips filed several patents for this design and formed the Phillips Screw Company. Phillips initially encountered difficulty in convincing manufacturers to produce his new screw. He persisted and finally persuaded the American Screw Company to license and manufacture his innovation. American Screw convinced General Motors to test Phillips screws on its assembly line, and GM used the new fastener to manufacture its 1936 Cadillac. It helped speed production, and was rapidly adopted by other Detroit car makers. By 1940, 85% of the screw manufacturing companies had secured a license from Phillips to produce his design.
Phillips drivers have an intentional angle on the flanks and rounded corners so they will cam out of the slot before a power tool will twist off the screw head, whereas the Pozidriv screws and drivers have straight sided flanks for increased torque and resistance to cam-out. The Pozidriv screwdriver and screws are also visually distinguishable from Phillips by the second set of radial indentations set 45 degrees from the cross recess. The manufacturing process for Pozidriv screwdrivers is slightly more complex. The Phillips driver has four simple slots cut out of it, whereas in the Pozidriv each slot is the result of two machining processes at right angles. The result of this is that the arms of the cross are parallel-sided with the Pozidriv, and tapered with the Phillips. This design is intended to decrease the likelihood that the Pozidriv screwdriver will slip out, provide a greater driving surface, and decrease wear.
The chief disadvantage of Pozidriv screws is that they are visually quite similar to Phillips, thus many people are unaware of the difference or do not own the correct drivers for them, and use incorrect screwdrivers. This results in difficulty with removing the screw due to damage to the recess, rendering any subsequent use of a correct screwdriver unsatisfactory. Phillips screwdrivers will fit in and turn Pozidriv screws, but will cam out if enough torque is applied, potentially damaging the screw head. The drive wings on a Pozidriv screwdriver will not fit a Phillips screw correctly, and are likely to slip or tear out the screw head.
