40 mm Aluminium Profile Range: Single, Four and Eight Slot Compared

01What does the range actually contain?

One slot system at a 40 mm pitch, across six section families. At 40 x 40 there are three variants that look similar and behave very differently: a single-slot section with three solid faces, a four-slot section, and an eight-slot section with two slots per face. Above that come the rectangular beams at 40 x 80, 40 x 120 and 40 x 160, each with a standard and a heavy wall version at the larger two sizes.

The slot pitch and the 8 mm mouth are common to all of them, so one accessory range covers the whole series. That is the practical value of staying inside one series even when the sections differ.

02Why is the eight-slot 40 x 40 weaker than the four-slot?

Because eight slots in the same 40 mm envelope removes more material than four. The eight-slot section is 1.70 kg/m against the four-slot’s 1.30 to 2.35, and the wall between two adjacent slots on the same face is only about 2 mm. The estimated second moment about either axis drops to roughly 4.5 cm4, against about 7 cm4 for a four-slot at 2.0 kg/m.

So the eight-slot is not a stronger four-slot. It is a four-slot with twice the fixing positions and less than two thirds of the stiffness. That is a legitimate trade for a frame that carries panels and cables, and a bad one for a frame that carries load.

03When is the single-slot section the right choice?

When the load path runs through solid metal rather than through a slot. The single-slot 40 x 40 has one 10.2 mm slot and three solid faces, at 2.10 kg/m. Those three faces are flat, uninterrupted and available for mounting a rail, a linear guide or a machined bracket, and there is no slot opening to distort under a bolt.

It is the section for a guide rail base, a carriage, or a member where a face has to stay flat for a running surface. It is a poor choice for a frame corner, because a corner needs slots on two adjacent faces.

• Single slot: rail bases, carriages, machined brackets, anywhere a solid face matters.
• Four slot: general framing, corners, guards, workbenches. The default.
• Eight slot: panel-heavy frames, cable routing, many small fixings, low load.
• Rectangular 40 x 80 and above: spans and loads, where the depth does the work.

04How does the moment of area step up through the range?

The numbers below are estimated on a 2.5 mm nominal wall with the slot openings deducted approximately, and they are what the selection actually turns on. Note that the step from 40 x 40 to 40 x 80 is a factor of about six, and from 40 x 80 to 40 x 120 about three.

05What does the selection matrix look like by span?

For a simply supported beam with a uniform load and an L/360 limit, the spans below are the practical range for each section at a light load. Above the upper figure the deflection governs and the section has to step up.

Two caveats. These assume a light uniform load; a heavy machine head changes the answer and the calculation has to be done. And they say nothing about vibration: a section that passes deflection at 2 m can still sit on a machine harmonic, which is a separate check with a separate answer.

06What five numbers should be on the enquiry?

A range enquiry needs the span and the load, because that is what picks the section. Everything else is secondary.

Span and support condition

clear span, simply supported or braced

Load and distribution

uniform or point, and the magnitude

Slot count needed

how many fixing faces, which decides between four and eight slot

Whether a solid face is needed

for a rail, a guide or a machined bracket

Finish and cut list

mill or anodised, and the lengths

Sections

40 x 40 single, four or eight slot, 40 x 80, 40 x 120, 40 x 160

Related sections and categories

The full range is listed under 40 Series Aluminium Profiles. For span tables on the most used beam, see the 40 x 80 mm load page, and for a gantry built from 40 x 80 and 80 x 120, the pairing page.