Phillips Head Screw

The origin of the lowly Phillips screw is an interesting one.

The history of metal fasteners go back to the 15th century. British toolmaker Joseph Whitworth devised the first screw in 1841 and American engineer produced the same in 1864.

Screws were very hard to produce, however, and required the manufacture of a conical helix.. The brothers Job and William Wyatt found a way to produce a screw on a novel machine that first cut the slotted head, and then cut the helix. Though their business ultimately failed, their contribution to low-cost manufacturing of the screw ultimately led to a vast increase in the screw and the screwdriver's popularity. The increase in popularity gradually led to refinement and eventually diversification of the screwdriver. Refinement of the precision of screws also significantly contributed to the boom in production, mostly by increasing its efficiency and standardizing sizes, important precursors to industrial manufacture.

Canadian Peter L. Robertson, though he was not the first person to patent the idea of socket-head screws, was the first to successfully commercialize them, starting in 1908. Socket screws rapidly grew in popularity, and are still used for their resistance to wear and tear, compatibility with hex keys, and ability to stop a power tool when set. Though immensely popular, Robertson had trouble marketing his invention to the newly booming auto industry for he was unwilling to relinquish his patents. Its use, however, remains popular in Japan.



Close-up of Robertson screw

Meanwhile, the Phillips screw drive was created by John P. Thompson, who, after failing to interest manufacturers, sold his design to businessman Henry F. Phillips who patented an improved version of a deep socket with a cruciform slot, today known as the Phillips screw. Phillips offered his screw to the American Screw Company, and after a successful trial on the 1936 Cadillac, it quickly swept through the American auto industry. With the Industrial Revival at the end of the Great Depression and the upheaval of World War II, the Phillips screw quickly became, and remains, the most popular screw in the world. A main attraction for the screw was that conventional slotted screwdrivers could also be used on them, which was not possible with the Robertson Screw. The original patent expired in 1966, but the Phillips Screw Company continued to develop improved designs.



Phillips screw head

Screw makers of the 1930s, however, dismissed the Phillips concept because it called for a relatively complex recessed socket shape in the head of the screw- as distinct from the simple milled slot of a slotted type screw. The Phillips screw design was developed as a direct solution to several problems with slotted screws: increased cam out potential; precise alignment required to avoid slippage and damage to driver, fastener, and adjacent surfaces; and difficulty of driving with powered tools.

The design is often criticized for its tendency to cam out at lower torque levels than other "cross head" designs. There has long been a popular belief that this was a deliberate feature of the design, to assemble aluminum aircraft and car parts without overtightening the fasteners.

Phillips drive bits are often designated by the letters "PH", plus a size code 0000, 000, 00, 0, 1, 2, 3, or 4 (in order of increasing size); the numerical bit size codes do not necessarily correspond to nominal screw size numbers.