For centuries, screws have been an integral part of human civilization, serving as essential fasteners in construction, machinery, and everyday objects.
Phase I: Prototypes and the Craftsman Era (before the 18th Century)
The Earliest “Screw”: Early screws were made of wood and used in grape pressing and olive oil pressing. After the advent of metal screws, they were primarily used in precision instruments (such as clocks and firearms) and fixtures.
The Birth of the Slotted Slot
During this period, slotted screws were the absolute mainstream. The reasons are simple：
- Easy to machine: A craftsman could create a simple slot in the screw head with a file.
- Simple Tools: A flat screwdriver (also known as a “slotted driver”) was sufficient, and manufacturing was also very easy.
- The Core Problem: The slotted slot had a fatal flaw: the screwdriver could easily slip out of the slot, damaging not only the workpiece and the screwdriver, but also the operator. This problem became unacceptable, especially on high-speed assembly lines.
Phase II: Industrialization and the Efficiency Revolution (Late 19th Century - Early 20th Century)
he Industrial Revolution and mass production created new demands for fasteners: efficiency and reliability.
The Invention of the Phillips Slot:
- In the 1930s, Henry Phillips patented and marketed a Phillips slot design.
- The core problem it addressed was slippage. This tapered Phillips slot design was self-centering, allowing the screwdriver to automatically stay centered.
- A more important feature was the cam-out effect: when the torque reached a certain level, the screwdriver head would be pushed out of the slot. This was an advantage in mass production because it prevented workers from overtightening and damaging the screw or the product (e.g., automotive panels, electronic product housings). This marked the birth of screw heads designed for mechanized assembly lines.
Phase III: Specialized Needs and Improved Performance (Mid-20th Century to Present)
As industries continued to segment, demands for screw performance grew. The cam-out effect of the Phillips slot became a disadvantage in applications requiring high torque. As a result, a series of new designs emerged:
Hexagon socket
- Appeared in the early 20th century, it became widely used after World War II.
- Advantages: Hexagon socket Provides high torque transmission capacity, eliminates slippage, and allows the screw head to sink into the workpiece, resulting in a clean appearance. Widely used in furniture, machinery, and molds.
Torx Socket:
- Invented by Camcar Textron in 1967.
- Design goal: Completely eliminate slippage and achieve higher torque than a hex socket. Its six-pointed star design evenly distributes force across six planes, significantly reducing wear on the tool head and extending tool life. It is now the preferred choice for high-torque applications in industries such as automotive, electronics, and aerospace.
Other Special Designs:
- Robertson Socket: Popular in Canada, it offers excellent anti-slip properties and is easy to operate with one hand.
- Tri-wing and Spanner Sockets: Primarily used in electronics and appliances to provide tamper-evident protection and prevent user disassembly.
Summary: Historical Driving Forces
Historically, the evolution of screw head types has been primarily driven by the following forces:
- From manual labor to machine tools: Slotted slots served the manual era, while Phillips slots catered to the assembly line era.
- The pursuit of efficiency and reliability: Phillips slots addressed slippage and efficiency issues; hexagon sockets and hexagonal sockets further addressed high torque and tool life.
- Specialization and safety needs: Different industries (furniture, automotive, electronics) have spawned screw heads that better suit their specific needs. Tamper-evident designs address security and warranty requirements.