Strut Aluminium Profile 40×40 mm 3-Slot T-Slot Extrusion Closed Face

OEM / ODM Available Free Sample Available ISO 9001:2015 EN 755-9 RoHS REACH

40 x 40 mm three-slot T-slot strut aluminium profile in 6063-T5 with one solid closed face, M6 slots on the other three faces and an M14 centre bore. For sealed, wipeable or labelled outward faces on guards and enclosures.

Wholesale Price $2.50 - $4.10 / m per m

Material	Aluminium
Alloy Grade	6063-T5
Temper	T5
Section Size	40 x 40 mm
Slot	M6 slot, 8 mm mouth, 3 slots, 30 mm pitch, one closed face
Length	6 m stock, cut to drawing to plus or minus 0.5 mm
Tolerance	EN 755-9 / GB/T 6892, wall plus or minus 0.15 mm
Surface	Mill finish / clear anodised / black anodised
MOQ	500
Lead Time	15-25 days after deposit for mill finish
Loading Port	Shanghai / Ningbo
Supply Ability	620 t per month
Payment Terms	T/T 30% deposit + 70% before shipment \| L/C at sight
Trade Terms	FOB \| CIF \| EXW
Certifications	ISO 9001:2015 \| EN 755-9 \| RoHS \| REACH

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Closed face · 40 series

A 40 x 40 three-slot strut profile is a 40 mm square T-slot extrusion with slots on three faces and one solid, closed face. It carries the same M6 slot geometry and the same O 12 mm centre bore tapped M14 as the four-slot version, and weighs about 1.70 kg/m. It is specified when one side of the member has to be a continuous flat surface rather than an open groove: a face for a gasket, a face that can be wiped clean, a face for a label or a logo, or a face that acts as an assembly reference.

The closed face is a feature, not a shortage. A bolt cannot enter from it, and that is the whole point: nothing can enter from it, including dust, wash water and the operator’s fingers. The cost is one fixing line and one direction of accessory access, plus a section that is no longer symmetrical, so the drawing has to say which face is closed and the assembly has to keep it consistent. Where none of that matters, the four-slot 40 x 40 is the more flexible member.

40 x 40 three-slot section: M6 slots on three faces, one solid closed face, 30 mm slot pitch, O 12 mm centre bore tapped M14.

What a closed face is actually for

On a four-slot section every face is a groove, and a groove is a dirt trap and a leak path. That is fine on a machine base, where nobody looks and nothing is washed. It is not fine on an enclosure that has to be sealed, a piece of equipment that is hosed down, or a frame that a customer sees every day. The closed face solves four different problems with the same piece of geometry.

A face that can be sealedA gasket, a foam strip or a bead of sealant needs a continuous flat surface to compress against. A slot cannot provide one: even with cover strip in place the joint line between strip and extrusion is a path for water. The closed face gives an uninterrupted 40 mm plane from end to end.

A face that can be wipedIn food, pharmaceutical and cleanroom equipment the requirement is a surface that can be cleaned, not merely one that can be reached. Powder and wash water collect in an open groove and are difficult to remove, so equipment in those industries is often built with the closed face outward and the slots inside the structure.

A face that can carry informationA label, a rating plate, a screen print or an engraved logo needs a flat surface. On a slotted face the label bridges the groove, wrinkles and peels at the edge. The closed face takes a printed or anodised graphic directly.

A face that can be a datumA closed face is a positive flat reference for squaring a frame: the section can be seated against a machined stop or a fixture face and clamped there without the slot lips interfering with the setting. It is also the face to use when the assembly is set out on a surface table.

What you give up

Three slots instead of four is a real reduction in flexibility, and it is worth being explicit about it rather than discovering it during assembly.

One fixing line per corner. A four-slot corner can be pulled from all four directions. A three-slot corner has one side that can only be fixed from the member it meets, so the joint detail has to be designed around the closed face rather than adapted to it on site.
Accessory access from three sides only. A T-slot nut is either slid in from the end of the member or dropped in at a slot opening. With one face closed there is one fewer direction for that, and on a long frame where the member is already fixed, it is the difference between dropping a nut in and dismantling the joint.
No cable exit through that face. Cable run inside the section can leave through an open slot or a machined hole. Through the closed face it has to be drilled, which breaks the anodising and, on a sealed enclosure, the seal.
A section that has a right way round. The closed wall is thicker than a slotted wall, so the section is slightly asymmetric: about 8.6 cm4 about the axis through the closed face against about 9.4 cm4 about the perpendicular axis. More visibly, a frame built with one member turned the wrong way will show a slot where the rest of the frame shows a flat face.

Property	40 x 40 three slot	40 x 40 four slot
Slots	3	4
Closed faces	1	none
Slot	M6, 8 mm mouth	M6, 8 mm mouth
Slot pitch	30 mm	30 mm
Centre bore	O 12 mm, tapped M14	O 12 mm, tapped M14
Moment of inertia, closed-face axis	approx. 8.6 cm4	approx. 9.2 cm4
Moment of inertia, other axis	approx. 9.4 cm4	approx. 9.2 cm4
Weight	approx. 1.70 kg/m	approx. 1.75 kg/m
Sealable face	one, end to end	none without cover strip

Orientation: the closed face has to be planned

Decide which face is outward and say so on the drawing Mark the closed face on the section view and on the layout. A supplier who is not told will treat the section as symmetrical, and a machinist who is not told will drill the closed face because it is the flat one.
Keep it consistent within a frame A frame has two sides and a customer can see both. If the closed faces are not kept on the same plane, the frame looks wrong from one end and the mistake cannot be corrected without rebuilding it.
Use the closed face for the seal, the slots for the structure The usual detail is the closed face outboard and carrying the gasket, with all the structural connections made on the three slotted faces inside the frame. That keeps the seal line continuous and the fasteners hidden.
Drill the closed face before anodising, or mask it Any hole through the closed face is a break in the anodising and, on a sealed enclosure, in the seal. Put those holes in the machining drawing so they are cut with the rest of the work and the area can be masked or the cut edges sealed.
Order cover strip for the three open slots If the frame is visible and the closed face is the reason for the choice, the three open slots should be closed with cover strip so the whole frame reads as flat faces. Mixing one flat face with three open grooves defeats the purpose.

Quick test: if the answer to “does anything have to be sealed, wiped, labelled or measured against this face?” is yes, specify the three-slot section and plan the orientation. If the answer is no, the four-slot section costs almost the same and is easier to build with.

Fixing and finishing the three-slot section

The three M6 slots take standard T-slot nuts, and corners are normally made with an angle bracket or a joining plate on the slotted faces. The closed face is not part of the joint, which is an advantage in a sealed assembly: the fasteners stay inside the enclosure and the outside stays a smooth, wipeable plane.

Feet and floor connections use a base plate or a levelling foot on the slotted faces. Panels are held with panel mounting elements where the panel is structural, and with a gasket against the closed face where the panel has to seal. Anodising is where the closed face earns its money: a 40 mm flat plane anodised in one batch gives a uniform, scratch-resistant outer surface that a slotted face cannot match.

Three-slot frames in service: a guard where the closed face carries the seal, and an automation cell where the closed faces are the outward, labelled surfaces.

Frequently asked questions

Can I still bolt through the closed face of a three-slot profile?

You can drill and machine it, and we do that to drawing, but there is no slot and no T-slot nut access, so the connection has to be a through-bolt or a tapped hole rather than a slot fixing. If the joint needs slot adjustment, make it on one of the three slotted faces.

What is a closed face actually used for?

A continuous flat surface for a gasket or sealant bead, a wipeable outer face for food, pharmaceutical and cleanroom equipment, a flat area for labels and screen-printed graphics, and a positive datum for squaring the frame during assembly.

Is the three-slot section weaker than the four-slot version?

No. It weighs about 1.70 kg/m against 1.75 kg/m and its stiffness is comparable: about 8.6 cm4 about the axis through the closed face and about 9.4 cm4 about the other, against about 9.2 cm4 both ways for the four-slot section.

Does the closed face change how the accessories fit?

The three slotted faces take the same 40-series T-slot nuts, brackets, feet and panel fixings as the four-slot section. The only difference is that one direction of access is closed, so accessories have to be loaded from the end of the member or through an open slot.

Can you supply it cut, tapped, drilled and anodised?

Yes. We cut to plus or minus 0.5 mm, deburr, tap the M14 centre bore and slot ends, drill and counterbore to drawing, and supply mill, clear anodised or black anodised. Send DWG, DXF, STEP or PDF.

Send the section drawing with the closed face marked

Tell us which face has to be solid and what it has to do, whether that is sealing, wiping or carrying a label. We will confirm the section, plan the orientation with you and quote the cut list, the machining and FOB pricing, with the closed faces protected in transit.

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