What is the difference between a key and a wedge?

What is a wedge?

Many people have used a wedge, even though they may not call it that. Think about one of those wooden blocks used as a doorstop. Or a piece of wood under a wobbly table or something you clamp between two things to keep it in place. You see wedges everywhere: in the home, in construction, when setting engineering structures. They are handy, simple and versatile.

What is a key?

A wedge is less well known, when in fact it is also just a type of wedge. The difference? A wedge has a right angle, so one side is straight and the other slopes. This allows you to hammer it firmly into a narrow opening. Wedges are often used to set machines, fix construction parts, or fix precast parts squarely, for example. They are designed to stay securely in place – without sliding back.

Yet fewer people are familiar with the wedge. That’s because wedges are often used in specialized applications, such as steel building, assembly and heavy construction. And because the word “wedge” is also used for other things (such as the tooth wedge on a shaft), people quickly get confused.

In short: you see a wedge everywhere – you don’t recognize a wedge until you know what to look for.

The advantages of a steel wedge:

• Very firm fixation: Due to its angled shape, a spigot stays firmly in place once it has been inserted – it works itself into place, so to speak.
• Reliable under high loads: wedges are ideal in applications where firm, permanent or semi-permanent fixation is required, such as steel columns, beams or machine parts.
• Prevents sliding: Because one side is straight, a key is less likely to slide back. This makes it more reliable under vibration or heavy loads. A wedge can slip under pressure.
• Suitable for tight joints: The right angle allows you to hammer a wedge in tightly between two surfaces without it bending or coming loose.
• Compact and powerful: A lot of force is still transferred with little material – the wedge sets wall-to-wall in a relatively small space.

Example:
Suppose you strike a spigot with about 5 kg of force at a 5° angle of inclination, that spigot secures with a force of about 560 N (about 57 kg of upward compression force).
That’s more than 11 times the force you struck with – purely due to the shape of the spigot.