2020 vs 2040 T-Slot Extrusion: Which Should You Use
A 2020 and a 2040 are the same extrusion in two shapes: 20 × 20 mm against 20 × 40 mm. Both are 20 series profiles, so they carry exactly the same slot, and every T-nut, bracket and printed part that fits one fits the other.
The decision is not about compatibility but about the cross-section: how far a member spans without support, what it carries, and which way round it sits in the frame. A bigger profile will not rescue a design that gets those wrong.
Dimensions here are approximate metric-standard values — wall thickness, corner radius and slot tolerance vary between suppliers, so measure your own profile. See the size chart for how.
What actually differs between 2020 and 2040
Line the two profiles up and almost every dimension matches, because the 20 series is one slot geometry. Only the outer rectangle changes.
| Property | 2020 | 2040 |
|---|---|---|
| Cross-section | 20 × 20 mm | 20 × 40 mm |
| Slot opening | 6.0 mm | 6.0 mm |
| Throat height | 1.5 mm | 1.5 mm |
| Inner channel width | 8.0 mm | 8.0 mm |
| Channel depth | 4.6 mm | 4.6 mm |
| Undercut per side | 1.0 mm | 1.0 mm |
| Centre bore | ⌀4.2 | ⌀4.2 |
The undercut is the gap a T-nut grabs: half the difference between the inner channel and the opening, so (8.0 − 6.0) / 2 = 1.0 mm. It is identical on both profiles, which is why the hardware swaps over — but a printed clamp that wraps a 20 mm face still has to be redrawn for a 20 × 40 mm section.
Where the 20 series sits in the range
The 20 series is the smallest of the four common slot families, and stepping up changes the slot as well as the size.
| Series | Cross-sections | Opening | Undercut per side | Centre bore |
|---|---|---|---|---|
| 20 series | 2020 · 2040 · 2060 | 6.0 mm | 1.0 mm | ⌀4.2 |
| 30 series | 3030 · 3060 | 8.0 mm | 1.5 mm | ⌀6.8 |
| 40 series | 4040 · 4080 | 8.0 mm | 1.5 mm | ⌀6.8 |
| 45 series | 4545 · 4590 | 10.0 mm | 2.0 mm | ⌀8.5 |
The 30 and 40 series share one slot profile, so they are interchangeable in exactly the way 2020 and 2040 are. The centre bore is the number to check first: on the 20 series it is ⌀4.2, which passes an M3 bolt and nothing larger.
When 2020 is enough
Most hobby and prototyping builds are 2020 builds, and they are fine: the slot is small enough that printed parts stay in scale, and brackets are cheap.
- Small frames and enclosures with no long unsupported member
- 3D printer enclosures, where the panels take the racking load
- Camera rigs, sensor mounts and light fixtures
- Printed brackets and hinges, designed around the 6.0 mm opening
The test is not the size of the frame but the length of its longest unsupported member and what hangs off it. A long 2020 beam with a load at mid-span will sag, and more corner brackets will not fix it — brackets stiffen joints, not spans.
When a 2040 earns its space
Step up when one of these is true, not because 2040 looks more serious.
- Longer unsupported spans, where sag grows quickly with span length
- A member that carries another member, such as a beam holding a gantry
- Mounting a motor or a moving load, where vibration finds the weakest point
- A frame that has to stay rigid, not merely hold its shape
The extra width also gives a bolted joint more room and makes it less likely to twist. Sometimes 2040 is not about load at all.
Orientation beats going one size up
Stiffness against bending rises steeply with the depth of the section, so orienting a rectangular profile the right way round matters more than choosing a slightly larger one. A 2040 standing with its 40 mm dimension vertical resists a downward load far better than the same profile lying flat.
Check the orientation before buying the next size up: a 2040 turned correctly usually beats a 2060 turned badly, and the same logic explains 4080 and 4590. A member is only as stiff as its weak direction, so if the load can arrive from two directions, use a square section such as 3030, 4040 or 4545.
When to leave the 20 series behind
If it is still not rigid enough after orienting it properly, the 20 series is the wrong family: heavier loads, longer spans, industrial guarding and machine bases belong in the 30, 40 or 45 series.
The practical trigger is usually hardware. The 30 and 40 series take M6 T-nuts and the 45 series takes M8, while the 20 series centre bore passes only an M3 bolt. The jump from 2020 to 3030 often happens for the fasteners, and the stiffness comes with it.
Mixing sizes in one frame is normal
A frame does not have to be one profile. Use the bigger sizes where the load path runs — base, feet, long horizontal members — and 2020 for uprights, cross-pieces and panel retainers. Anything bolted directly to another member has to be in the same slot family, so plan the transition between a 2020 and a 4040 at the design stage; a connector or a printed adapter is the easiest answer.
What a bigger profile costs you in printed parts
A bracket that wraps a 20 × 40 mm section uses more material and takes longer to print than one for a 2020, so bolting a 2020 bracket to a larger profile is often cheaper than printing an oversized part. In a printed joint the plastic is almost always the weak link, not the extrusion.
Frequently asked questions
Do 2020 and 2040 use the same T-nuts and brackets?
Yes. Both are 20 series profiles, so every T-nut, bracket and printed part that fits a 2020 fits a 2040 with no changes at all. Only the outer cross-section is different.
What is the difference between 2020 and 2040 extrusion?
The cross-section. A 2020 is 20 × 20 mm and a 2040 is 20 × 40 mm, so the 2040 is twice as wide in one direction at the same 20 mm depth. The slot dimensions are identical on both.
Is 2040 stronger than 2020?
It can be, but only if it is loaded the right way round. Stiffness against bending rises steeply with the depth of the section, so stand the 40 mm dimension vertically against a downward load. Turned the other way, a 2040 behaves much more like a 2020.
When should I move up to the 30 or 40 series?
When the span or the load outgrows the 20 series, or when you need bigger hardware. The 20 series centre bore is ⌀4.2, which only passes an M3 bolt. The 30 and 40 series take M6 T-nuts and the 45 series takes M8.
Model the frame before you cut aluminum
Pick 2020 or 2040 in the generator, set the lengths, and export the profiles at size, with 45° mitre cuts and drilled holes if you need them. It is quicker to find a member mounted the wrong way round on screen than after it has been cut.
Open the aluminum extrusion generator →
- Aluminum extrusion size chart — slot dimensions
- Aluminum extrusion connectors — joint types
- T-slot nut dimensions — what fits what
- 3D printed T-nut — printing one
- 45° mitre cut extrusion — clean corners
- Aluminum extrusion generator — build the model