How does a rivet fasten sheets together?

1. Two metal sheets lie on a bench. Nothing holds them, so one push makes the top sheet slide away. We need something to lock them together.
2. First we drill one hole straight through both sheets, so the two holes line up exactly. The hole is just a tiny bit wider than the rivet.
3. A rivet is a short metal pin with a round head on one end. It slides through the holes until the head stops it. The plain end, called the tail, sticks out.
4. A heavy block holds the head still while a hammer hits the tail. Each hit squashes the tail shorter and wider, until it becomes a second head.
5. Now the rivet has a head on both sides, and both are wider than the hole. The sheets are squeezed in between. Pull them, and nothing moves.
6. Rows of rivets hold together bridges, ships and airplanes, and tiny copper rivets even strengthen the pockets of jeans. Each one is a pin with two heads.

This joint has been sliced down the middle. Tap each part to see what it does.

• Head. The head is shaped when the rivet is made. It is wider than the hole, so it stops the rivet on one side of the sheets.
• Shank. The shank is the smooth middle of the rivet. Hammering makes it swell a little, so it fills the hole and the sheets cannot wiggle.
• Squashed tail. The tail started as a plain end sticking out. Hammering squashed it into a second head, wider than the hole, so it can never slide back.
• Two sheets. The two sheets are trapped between the rivet's two heads. They cannot lift apart, and they cannot slide.
• Hammer. The hammer hits the tail many times. In factories a rivet gun does the same job, hitting very fast with a rattling sound.
• Holding block. A heavy block presses against the head. Without it the hammer would just knock the rivet back out of the hole.

Tap the hammer to squash the rivet's tail. Try the pull test early, and again when you finish. Then try a short tail and a long one.

Experiment: What happens if you pull the sheets while the tail is still thinner than the hole?

1. Hit the rivet once or twice, then press Pull test.
2. Keep hammering until the tail is wide and flat. Pull again.
3. Start over with a short tail, then a long tail. Which one makes a good head?

What we found: A rivet only grips when its tail has been squashed wider than the hole. Before that, the sheet slides off. A tail that is too short has too little metal to make a head, and one that is too long bends over instead of squashing flat.

Turn on JavaScript to try it yourself.

Put a rivet in every hole and hammer each one just enough. Then hang the load. Will your joint hold?

A rivet is one of the oldest ways to join metal. It is a short pin with a head already made on one end. You drill a hole through both sheets, push the rivet through, and then squash the plain end, called the tail, until it spreads into a second head.

Why does squashing work? Metal can bend and flow without breaking if you push it hard enough. The hammer does not remove any metal. It just moves it sideways, so the tail gets shorter and wider. Once the tail is wider than the hole, it cannot go back through.

The length of the tail matters. If too little sticks out, there is not enough metal to make a proper head. If too much sticks out, the tail bends over like a bent nail instead of squashing flat. Rivet workers leave about one and a half times the rivet's width.

Rivets are very good at stopping sheets from sliding over each other, and they do not shake loose the way a screw can. That is why you see neat rows of them on airplanes, old steel bridges, ships and even the corners of jeans pockets. Our button comparison is not perfect, though: you can undo a button, but a rivet is there for good.

Key words

Rivet

A metal pin with a head, squashed at the other end to lock sheets together.

Shank

The smooth body of the rivet that sits inside the hole.

Driven head

The second head, made by squashing the tail.

Plastic deformation

When metal is pushed so hard that it changes shape and stays that way.

Shear

A sliding force, like two sheets trying to slip past each other.

Clearance

The tiny gap between the rivet and the hole before the rivet is driven.

Check your thinking

1. Why can't a finished rivet slide back out of its hole?

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   Both ends are now wider than the hole. The factory head is on one side and the squashed tail is on the other. Both are wider than the hole.

2. What happens to the tail's metal when it is hammered?

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   It moves sideways, so the tail gets shorter and wider. No metal is lost. The same metal is pushed into a new shape.

3. A rivet's tail barely pokes out of the hole. What will happen when you hammer it?

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   There is not enough metal to make a wide head, so it stays loose. The head is made only from the metal that sticks out. A short tail cannot spread far.

4. Why is a heavy block held against the rivet's head while the tail is hammered?

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   So the hammer squashes the tail instead of knocking the rivet out. With nothing behind it, the rivet would just slide back through the hole.

5. One rivet has twice the diameter of another, made of the same metal. About how much more sliding force (shear) can it resist?

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   Four times as much. Shear strength depends on cross-section area, which grows with the square of the diameter: 2 squared is 4.

6. Why do airplanes use rivets instead of only screws?

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   Rivets do not shake loose when things vibrate. A screw can slowly turn and work loose. A rivet has no thread to turn, so it stays put.