# Aluminum Extrusion Profile 8 40x40

How an 8 40x40 aluminium extrusion profile hides its T\-slot nut and locks bars into a right\-angle corner with a bracket and screw\.

By M\. Wendelin

Topic: Engineering

[Open the interactive Jig](https://ask.jig.com/j/d3ZUBXZx8Yqd)

## Transcript

### 1. A bar with a secret shape

This silver bar is an aluminium extrusion profile, called 8 40x40\. It is made by pushing hot aluminium through a shaped hole, like toothpaste from a tube\. Look at its end: the shape inside is what makes it so useful\. Drag to turn the bench\.

Builders use these bars for machines, 3D printers, workbenches and robot frames\.

### 2. Forty by forty

The name tells you the size\. The bar is exactly 40 mm wide and 40 mm tall, about as wide as a matchbox is long\. Its outer corners are gently rounded, with a 4 mm radius, so they are kind to hands\.

Bars are cut to any length you need, usually to within about 1 mm\.

### 3. The 8 mm slot

Every face has a long groove called a T\-slot\. Its opening is 8 mm wide, and that is what the 8 in the name means\. Behind the narrow opening the slot widens and goes about 12 mm deep, like a hidden tunnel running the whole length\.

Parts for an 8 mm slot will not fit a 10 mm slot system, so the slot size matters when you shop\.

### 4. Hollow and light

The profile is not solid\. Four hollow chambers sit in the corners and a 6\.8 mm hole runs through the centre\. Thin walls and cross braces make it stiff while saving metal, so a metre weighs only about 1\.4 kg\.

The centre hole can be threaded for an M8 screw, so another part can be fixed to the bar's end\.

### 5. Meet the T\-slot nut

A T\-slot nut is a small steel block with a threaded hole\. It is too wide to come out through the 8 mm opening, but it slides along the hidden tunnel\. We have cut the bar open so you can see inside\. Slide one in from the end\.

M8 means the screw thread is 8 mm across\.

### 6. Clamp it tight

Now a corner bracket sits on top and an M8 screw goes through it into the nut\. As the screw turns, it pulls the nut up against the slot's lips\. The lips are squeezed between nut and bracket, and friction holds everything still\.

Loosen the screw and the nut can slide again, so every part stays adjustable\.

### 7. Build a corner

A second bar stands on the first\. Its own nut waits in its slot, and a screw through the bracket's other leg locks the two bars together at a perfect right angle\. No welding and no drilling is needed\.

### 8. One system, endless frames

The same nuts, screws and brackets fit every slot on every face, anywhere along the bar\. Repeat the corner and a frame appears\. Take it apart and the pieces build something new\. Everything lines up on a 40 mm grid\.

That is modularity: a few standard parts that combine in countless ways\.