The History of Socket Set Screws
The History of the Socket Set Screw is Tied Closely to the Rise of Industrial Machinery & Factory Safety
Before the Socket Set Screw
The set screw itself is much older than the hex socket version. Its basic job is simply to screw it into one component until the point end of the screw presses against another component, locking the two together. For example, a pulley could be mounted on a rotating shaft and held in place by a set screw.
Early industrial machinery commonly used square headed set screws. The problem was that the square head stuck out from the rotating shaft or collar. That created a serious safety hazard, loose clothing, fingers, or other objects could catch on the protruding head of the screw while the machinery was running.
The socket set screw emerged commercially in the United States around 1910–1911.
Two Developments Are Particularly Important
- William G. Allen, founder of the Allen Manufacturing Company in Hartford, Connecticut, developed what was marketed as the “Allen Safety Socket Set Screw.”
- Howard T. Hallowell Sr. and the Standard Pressed Steel Co. ( SPS ) independently developed a similar hex socket system around 1911.
Allen manufacturing had patented a method for forming a hexagonal socket into the body of the set screw in 1909, and Allen manufacturing was advertising the safety of socket set screw by 1910.
The important innovation wasn’t really the idea of using a screw to hold something in place, it was putting the hex recess inside the screw body, allowing the entire screw to sit flush or below the surface of the tapped hole.
Where the “Allen” Name Comes From
The Allen Hex key was developed as the companion driving tool for Allen’s safety socket set screws.
The Allen Manufacturing Company was founded by William G. Allen in 1910, and its early product was specifically the safety of socket set screw with an internal hex socket. and the corresponding L-shaped Allen hex wrench.
Why the Hex Socket Was So Useful
The internal hex solved several problems at once:
1. Safety:
There was no external head sticking out to catch clothing or body parts. This was particularly valuable on rapidly rotating shafts, pulleys, gears, and shaft collars. The early 20th-century push for industrial safety was a major driver.
2. It could fit where a wrench couldn’t:
A conventional wrench needs room around the outside of the fastener. A hex key only needs access to a small area. That made socket screws especially useful in tight situations.
3. The socket end of the set screw could remain flush or below the surface:
This was particularly important for rotating components. You could tighten the screw into a collar, gear, pulley, etc., without leaving a dangerous projection.
4. Good torque in a tiny package:
The hexagon socket allows the hex Allen wrench with its’ six flat surfaces to seat itself against the six flat surfaces within the socket to produce the recommended tightening torque.
What About the “Cup Point”?
The screw you’re probably picturing today, the little headless screw with an internal hex and a concave/cup-shaped tip, is a later refinement of the basic concept.
The cup point on the set screw produces a deeper penetration on the surface of the shaft to secure the two components together. The original flat point design would only seat itself against surface.
The Cup point design was subsequently developed in numerous forms and a U.S. patent specifically concerning improvements to the cup-point set screw was filed by Calvin O. Brown in 1953 and granted in 1957.
Interesting Fact: “Grub screw” is another common name, particularly in British usage.
Conclusion
“Allen screw” is a commercial/trade name, the derived term referring to the hex socket drive associated with Allen Manufacturing. So, the little screw that seems almost trivial today is a product of a very practical early 20th-century problem. How do you fasten something securely to a rotating shaft withoutleaving part of the screw sticking out of the tapped hole that can grab a worker? That safety problem helped turn the socket set screw into a major industrial fastener.