Engineering · slot geometry, series, hardware fit

Slot Dimensions Explained: 6 mm, 8 mm and 10 mm T-Slots

A 45 × 90 mm six-slot 6063-T5 bar weighs 4.10 kg/m with I ≈ 68 cm⁴ on the strong axis, and under EN 755-9 the wall sits within ±0.15 mm while straightness is held to 1.5 mm/m. Those numbers sit on the drawing; the slot mouth — 6 mm, 8 mm or 10 mm — decides which nut actually fits.

Slot family: 6 mm / 8 mm / 10 mm mouths
Example section: 45 × 90 mm, 4.10 kg/m, I ≈ 68 cm⁴
Tolerance base: EN 755-9 wall ±0.15 mm
Read: 8 minutes

Three silver anodised aluminium T-slot extrusions showing cross-sections on a factory inspection bench

Short answer

Metric T-slot framing uses three mouth widths: 6 mm on the 20 series, 8 mm on most 30 and 40 series, and 10 mm on the 45 series and heavier frames. A 2020 profile is 20 × 20 mm with a 6 mm slot; European workbenches most often land on 8 mm / 40-series hardware. Choose 8 mm when M6–M8 fasteners and mid-span loads are enough; choose 10 mm when the joint needs a larger nut, a thicker lip and a heavier envelope. Copy the geometry table below into the drawing, then hold extrusion to EN 755-9 (wall ±0.15 mm, straightness 1.5 mm/m, twist 2°) and secondary cuts to length ±0.5 mm, hole position ±0.2 mm and end square within 0.3 mm.

Slot mouth width — not the outer envelope — decides which T-nut and bolt the profile will take.

What is the standard slot for a workbench in europe

For a European industrial workbench the default is an 8 mm slot on a 40-series envelope, because that geometry takes the M6–M8 hardware most fixture shops already stock.

Light display or lab benches sometimes drop to 20-series / 6 mm when the span is short and the load is a few tens of kilograms. Heavy welding or robot cells step up to 45-series / 10 mm so the lip and the nut can carry higher joint preload. The table maps the mouth to the series a buyer will actually find in a European catalogue; the outer size can be 30 × 30, 40 × 40, 40 × 80 or larger without changing the fastener family once the mouth is fixed.

Use case	Typical series	Slot mouth	Usual fasteners	Verdict for a workbench
Light lab / display bench	20 series	6 mm	M3–M5	Only if spans stay short
Standard assembly bench	30 / 40 series	8 mm	M6–M8	European default
Heavy fixture / welding table	40 / 45 series	8 or 10 mm	M8	Prefer 10 mm if reuse is long
Robot cell / gantry base	45 / 50 series	10 mm	M8–M10	10 mm slot
Guard frame only	20 / 30 series	6 or 8 mm	M5–M6	6 mm acceptable
Mixed plant standard	40 series	8 mm	M6–M8	Keep one hardware kit

What is the slot width on a 2020 profile

A 2020 profile is 20 × 20 mm and uses a 6 mm slot mouth; the inner channel is typically about 8 mm wide and 4.6 mm deep with a centre bore near Ø4.2 mm for an M5 tap.

The name is the envelope in millimetres, not the slot. The same 6 mm mouth appears on 20 × 40 and 20 × 60 bars in the same family. Heavier envelopes move the mouth: 30 and most 40 series use 8 mm; 45 series uses 10 mm. Use the geometry grid below as a drawing paste-in; confirm critical fits on a sample because lip thickness and undercut vary slightly between dies even when the mouth is nominally identical.

Series / section	Envelope	Slot mouth	Channel (typ.)	Centre bore (typ.)
20 series / 2020	20 × 20 mm	6.0 mm	8.0 × 4.6 mm	Ø4.2 mm (M5)
20 series / 2040	20 × 40 mm	6.0 mm	8.0 × 4.6 mm	Ø4.2 mm
30 series / 3030	30 × 30 mm	8.0 mm	11.0 × 6.2 mm	Ø6.8 mm (M8)
40 series / 4040	40 × 40 mm	8.0 mm	11.0 × 6.2 mm	Ø6.8 mm
45 series / 4545	45 × 45 mm	10.0 mm	14.0 × 7.8 mm	Ø8.5 mm (M10)
45 series / 4590	45 × 90 mm	10.0 mm	14.0 × 7.8 mm	Ø8.5 mm

How do i choose between 8 mm and 10 mm slot profiles

Choose 8 mm when M6–M8 hardware and mid-range joint loads are enough; choose 10 mm when you need a larger nut, a thicker lip and a heavier series for long spans or repeated rebuilds.

An 8 mm mouth is the volume standard on 30 and 40 series machine frames and workstations. A 10 mm mouth appears on 45-series and many heavy 40/50 variants, and it is the safer pick when connectors stay installed for years under vibration. The outer envelope still sets bending stiffness: a 45 × 90 mm six-slot bar at 4.10 kg/m with I ≈ 68 cm⁴ out-stiffs a light 40 × 40 even before the slot is considered. Match the fastener first, then pick the envelope for span and mass. If an existing plant already standardises on one mouth, stay on that mouth so T-nuts and brackets remain interchangeable.

How to read the table

Read each row as three decisions: envelope for stiffness, mouth for hardware, and bore for end-tapping or internal anchors.

The first columns fix the outer size you draw; the mouth column fixes the nut; the bore column fixes whether an M5, M8 or M10 tap is realistic. Tolerances sit outside the geometry table: extrusion wall ±0.15 mm, straightness 1.5 mm/m and twist 2° under EN 755-9; after cutting, length ±0.5 mm, hole position ±0.2 mm and end square within 0.3 mm. Weight per metre is area × 2.70 g/cm³; the 45 × 90 example at 4.10 kg/m is the figure to put on a BOM when that section is specified. Die cost and lead time are separate commercial lines — see how die cost amortises per meter, minimum order with a new die, die making adds 7–12 days and who owns the die.

RFQ checklist — slot dimensions on the drawing

Series and envelope — e.g. 4040 or 45 × 90 mm six-slot.
Slot mouth — 6, 8 or 10 mm, with a measured sample if hardware is reused.
Hardware set — T-nut size and whether core-hole anchors are used.
Alloy / temper — usually 6063-T5 for framing.
Mass and inertia — kg/m and I if the span is structural.
Tolerances — EN 755-9 plus cut/hole call-outs.

Put the mouth width on the drawing next to the envelope. A 40 × 40 label without “8 mm slot” leaves the fastener ambiguous.

Related on this site

how die cost amortises per meter — tooling share inside the metre price
minimum order with a new die — 150 m existing vs 500 m new
die making adds 7–12 days — calendar before first bars
who owns the die — tooling title after the trial

Terms used in this article

Slot mouth: The narrow opening at the face of a T-slot; the dimension a nut must pass.
Series: The envelope family (20, 30, 40, 45…) that usually locks the mouth width.
Centre bore: The longitudinal hole used for end tapping or internal anchors.
EN 755-9: European extrusion tolerance standard for wall, straightness and twist on the lengths we ship.
Moment of inertia (I): Section property that sets bending stiffness for a given span and load.

Questions buyers ask

What standard are the tolerances measured against?

Extrusion wall, straightness and twist follow EN 755-9: wall ±0.15 mm, straightness 1.5 mm/m and twist 2° on the lengths we ship. Cut and hole work after extrusion is held to cut length ±0.5 mm, hole position ±0.2 mm and end square within 0.3 mm. Slot mouth itself is a catalogue geometry, so quote the series and measure a sample when hardware fit is critical.

Can you supply a mill certificate?

Yes. Mill certificates for 6063-T5 (or the alloy on the order) ship with the batch and list heat number, chemistry and temper. For a drawing hand-off, ask for the certificate together with the section weight per metre so the mass on the BOM matches the invoice kilograms.

What is the minimum wall thickness?

On standard T-slot catalogue dies the thinnest wall is set by the series tooling, typically about 1.5 mm on light 20-series and thicker on 40 and 45 series. Custom dies can go thinner, but below about 1.2 mm the press window narrows and surface quality suffers. Put the critical wall on the drawing rather than assuming the catalogue minimum.

How is weight per metre calculated?

Weight per metre is cross-sectional area times density 2.70 g/cm³ for 6063, expressed as kg/m. A 45 × 90 mm six-slot section at 4.10 kg/m is the worked example on this page; Ix around 68 cm⁴ comes from the same nominal section. Use the mill mass on the certificate for freight, not a rounded catalogue figure.

Also searched as: t-slot dimensions, 6 mm 8 mm 10 mm slot, 2020 profile slot width, european workbench aluminium slot, 4040 8 mm slot, 4545 10 mm slot, t-slot geometry table, aluminium profile slot mouth.

Send the series and the hardware you must fit

Attach the section code or a dimensioned end view, name the T-nut or anchor you reuse, and we will confirm mouth, bore and mass against a sample before the die or cut list is locked.

Request a quote