# Clamp Plate Explained

How a steel clamp plate uses its bone\-shaped outline and a stepped counterbore hole to press a bushing firmly onto a block\.

By curious\-comet\-ca21571a

Topic: Engineering

[Open the interactive Jig](https://ask.jig.com/j/qF1fsY5SLC00)

## Transcript

### 1. Meet the clamp plate

This thick steel plate has one job: to hold another part firmly in place\. Here it holds down a bronze sleeve, called a bushing, that a spinning shaft runs through\. Let's find out how its shape does that job\.

Drag the scene to look around\. Pinch or scroll to zoom\.

### 2. Shaped like a bone

The plate is 380 millimetres long, a little longer than a school ruler, and 20 millimetres thick\. A round hub sits in the middle and a round lobe at each end\. The arms between them are slimmer, which saves steel where less strength is needed\.

### 3. The big hole

The hole in the hub is 100 millimetres across\. The bushing passes through it, so the plate fits around the bushing like a ring around a finger\.

The symbol Ø means diameter: the distance straight across a circle\.

### 4. A hidden step

Turn the plate over and slice it in half, and a step appears\. The hole widens to 135\.6 millimetres for the first 10 millimetres\. Engineers call this a counterbore: a wider, flat\-bottomed hole cut on top of a smaller one\.

The green stripes copy how engineering drawings mark cut metal\.

### 5. The step grips the collar

In use, the step faces down\. The bushing has a wide collar that fits snugly into the step\. When the hinged bolts swing up and the nuts are tightened, the plate presses the collar onto the block, so the shaft can spin but the bushing cannot move\.

### 6. Open slots, quick release

Each end hole opens into a slot 20 millimetres wide\. Loosen the nuts a few turns and the hinged bolts tip out through the slots, so the plate lifts free and no nut has to come off\. Bicycle frames use open slots in the same way, so a wheel can drop out quickly\.

### 7. Read it like a drawing

Engineers describe the plate with a drawing full of numbers\. The end holes are 150 millimetres from the centre, and R means radius, half of a circle's width\. Every number tells a machinist exactly where to cut, and now you can read them too\.