1. The square head of Allen wrench is prismatic, as shown in the figure below.
2. The ball head of the Allen wrench is nearly spherical, as shown in the figure below.
The key to the survival of Allen wrench and its becoming an indispensable and effective tool in industrial manufacturing lies in its uniqueness and many advantages:
1, very simple and light.
2. There are six contact surfaces between the Allen screw and the wrench, which are fully stressed and not easy to be damaged.
3. It can be used for screwing screws in deep holes.
The diameter and length of the wrench determine its torque.
Extended data:
Speaking of the origin of Allen key, we must start with Allen key. In some non-English-speaking countries in Europe, people call "Allen key" "Unbrako key", which is actually the earliest brand of hexagon socket head screws. It was founded by American SPS Company around 19 1 1.
SPS Company imported an inner quadrangular screw from England earlier, but the price was very expensive. In order to save money, SPS decided to produce it by itself. Hallowell, the founder of SPS, said in his memoirs: "We started to try to make some square-hole screws similar to those in Britain, but soon found that such screws would not be accepted in the United States.
So the company decided to add hexagonal holes to the screws. Hallowell's explanation of this history is vague, but later generations speculated that SPS was modified to avoid patent disputes of internal quadrangular screws. In a word, SPS Company began to produce this new type of hexagon socket head screws and registered the trademark "Unbrako", which is taken from the homonym of "unbreakable", meaning "unbreakable".
Later, hexagon socket head screws gradually replaced internal four-corner screws and became a new industry standard, which was widely used in automobile, airplane, machinery, furniture and other manufacturing industries.