Aluminum Extrusion Size Chart

The number in a profile name is its cross-section in millimetres, so a 2020 is 20 × 20 mm and a 4040 is 40 × 40 mm. The 20 series uses a 6 mm slot opening, the 30 and 40 series both use 8 mm, and the 45 series uses 10 mm.

The table below is the metric-standard approximation used by most European suppliers. It is the same set of values the generator uses to build its models, so a part you print from here matches the numbers on this page.

Nothing here replaces a caliper. Section sizes are standardised, but wall thickness and slot tolerance are not — see how to measure your own profile.

Slot dimensions by series

Every number is in millimetres. "Undercut" is how far the channel widens beyond the opening on each side — the gap a T-nut locks into.

Series	Common cross-sections	Slot opening	Throat height	Channel width	Channel depth	Undercut per side	Centre bore
20 series	2020 · 2040 · 2060	6.0	1.5	8.0	4.6	1.0	⌀4.2
30 series	3030 · 3060	8.0	2.0	11.0	6.2	1.5	⌀6.8
40 series	4040 · 4080	8.0	2.0	11.0	6.2	1.5	⌀6.8
45 series	4545 · 4590	10.0	2.5	14.0	7.8	2.0	⌀8.5

Throat height is how deep the narrow opening is before the channel flares out. It matters when you design a part that has to pass through the slot: a printed T-nut needs to fit through the 6 mm gap and then turn, so its neck has to be thinner than the opening and no taller than the throat.

How to read a profile name

Once you know the pattern, every name is self-explanatory:

2020 — 20 × 20 mm square
2040 — 20 × 40 mm rectangular
2060 — 20 × 60 mm rectangular
3030 — 30 × 30 mm square
4040 — 40 × 40 mm square
4545 — 45 × 45 mm square
4590 — 45 × 90 mm rectangular

Rectangular versions keep the slot of their series, so a 2040 uses the same 6 mm slot as a 2020 and takes the same nuts and brackets. That is why you can mix square and rectangular profiles in one frame without changing hardware.

Which series should you use?

Series	Typical use
20 series	Small mechanisms, 3D printer frames, camera rigs, sensor mounts, light enclosures. The default for printed parts.
30 series	Medium frames, workbenches, machine guards, small robotics. A good middle ground when 2020 feels flimsy.
40 series	Larger frames, machine bases, long spans, anything that has to stay rigid under load.
45 series	Heavy frames, industrial guarding, long unsupported spans.

A larger cross-section carries more load because there is more material, but the real limit is wall thickness, alloy and how the joint is made — not the section size alone. For anything structural, use the load data from your supplier rather than the numbers here.

How to measure your own profile

Supplier tolerances are real, and a printed part that has to clip into a slot is not forgiving. Five minutes with calipers saves a failed print:

Outer cross-section. Confirm the outside really measures what the label claims, rather than trusting the nominal size.
Slot opening at its narrowest point — the gap between the two lips, not the channel behind them.
Channel width at its widest, measured inside the undercut.
Throat height: how far in you can push the caliper jaws before they open up into the channel.
Centre bore, if the profile has one and you plan to tap it or run a bolt through it.

Then tell the generator those numbers instead of trusting the preset. Every dimension above is editable, and the fit clearance setting is there for exactly this reason: leave 0.1–0.2 mm for a tight fit and 0.3–0.5 mm for a loose one.

Designing a printed part for a slot

The two numbers people get wrong are the throat height and the undercut.

A T-nut has to enter through the opening and then rotate so its flanges sit in the undercut. That means the flange has to be narrower than the opening to get in, wider than the opening to stay in, and thin enough to fit inside the channel depth. If it jams halfway, the throat height is usually the culprit — it is only 1.5 mm on the 20 series.

Print orientation matters just as much: a T-nut printed flat has its layer lines running across the flange, which is the direction it gets pulled. Standing it up puts the layers along the load instead.

Frequently asked questions

What does the number in 2020 or 4040 mean?

It is the cross-section size in millimetres. A 2020 is a 20 x 20 mm profile and a 4040 is 40 x 40 mm; a 2040 is 20 mm by 40 mm. The first pair of digits is one side, the second pair is the other.

What is the slot opening of a 2020 profile?

2020 profiles use the 20 series slot: a 6 mm opening, an inner channel 8 mm wide and 4.6 mm deep, and a 1 mm undercut on each side. That undercut is what a T-nut or hammer nut grabs onto.

Do 3030 and 4040 use the same slot?

Yes. The 30 and 40 series share one slot profile: an 8 mm opening, an 11 mm channel, 6.2 mm deep, with a 1.5 mm undercut per side. Only the outer cross-section differs, so the same T-nut fits both.

Are these dimensions the same for every manufacturer?

No. These are metric-standard approximate values. Wall thickness, corner radius and slot tolerance vary between suppliers, so measure your actual profile with calipers before designing a part that has to fit it.

How do I measure a T-slot profile?

Measure the outer cross-section with calipers, then the slot opening at its narrowest point and the channel at its widest. Also measure how deep the narrow opening goes before the channel flares out, because a printed T-nut has to pass through that gap to lock in.

Which series should I use for a 3D printed project?

The 20 series is the usual choice: it is the cheapest, the most widely available, and its 6 mm slot is small enough that a printed part still looks in scale. Move up to the 30 or 40 series when the frame has to span a distance or carry real weight.

Build the part for your profile

The generator turns these numbers into an STL you can print straight away: profiles at any length with 45° mitre cuts and drilled holes, plus corner brackets, T-nuts, hidden joiners and splice plates. Pick a series, check the dimensions against your own profile, and export.

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