Aluminium Inner Bracket with Top Thread M5 M6 M8 for 20 to 40 mm T-Slot Profiles

OEM / ODM Available Free Sample Available ISO 9001:2015 RoHS REACH

A hidden inner bracket with top thread for aluminium T-slot profiles, supplied in M5 x 6, M6 x 8 and M8 x 10 to suit 6.2, 8.2 and 10.2 mm grooves. No visible fixing and no profile end machining.

Wholesale Price $0.22 - $0.68 / pc per pc

Material	Zinc alloy or aluminium body with steel set screw
Alloy Grade	Zamak 3 die casting or 6063-T5 body, 304 stainless set screw
Temper	custom
Section Size	30 x 21.2 x 8 mm body with a 1.4 mm flange
Slot	Suits 6.2, 8.2 and 10.2 mm grooves, M5 to M8 thread
Length	Stocked to suit 20, 30 and 40 series profiles
Tolerance	ISO 8062 die casting \| ISO 2768-m machining
Surface	Zinc plated or natural finish
MOQ	500
Lead Time	15-25 days after deposit
Loading Port	Shanghai / Ningbo
Supply Ability	1.5 million pieces per month
Payment Terms	T/T 30% deposit + 70% before shipment \| L/C at sight
Trade Terms	FOB \| CIF \| EXW
Certifications	ISO 9001:2015 \| RoHS \| REACH

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Connecting elements · Hidden joints

An inner bracket with top thread is a hidden profile connector that slides into the groove of both members and is locked by a set screw driven down onto the groove floor. The bracket measures about 30 mm long, 21.2 mm high and 8 mm wide, with a 1.4 mm locating flange along each edge, and it is made in three sizes: M5 x 6 for the 6.2 mm groove of 20 series, M6 x 8 for the 8.2 mm groove of 30 series and M8 x 10 for the 10.2 mm groove of 40 series.

The reason this joint works is worth understanding, because it is not a bolted joint at all. A T-slot has an undercut: the mouth of the groove is narrower than the cavity behind it, and the bracket’s 1.4 mm flange sits in that undercut. When the set screw is tightened it pushes the bracket body down and away, and because the flange is trapped behind the narrow mouth, the bracket is wedged against the profile. The joint is held by the geometry of the slot, not by the tension in the screw.

Hidden inner bracket with top thread for aluminium T-slot profiles shown in M5x6, M6x8 and M8x10 sizes with the locating flange — The inner bracket: 30 mm long, 21.2 mm high, 8 mm wide, with a 1.4 mm flange that engages the groove undercut.

The joint is held by the undercut, not by the screw

Every T-slot profile has a groove whose mouth is narrower than the cavity behind it. On the 20 series the mouth is 6 mm against a 6.2 mm groove; on the 30 series it is 6 mm against 8.2 mm; on the 40 series it is 8 mm against 10.2 mm. That undercut is what a T-slot nut engages with when you slide it in from the end, and it is what this bracket uses as well.

The bracket body is inserted into the groove of the first member, with its 1.4 mm flange sitting behind the narrow mouth. The second member is brought up to it, and a set screw is driven down through the top thread until it bears on the groove floor. Tightening the screw pushes the bracket body sideways and downwards, and because the flange cannot escape through the mouth, the bracket jams against the undercut. Nothing protrudes, and there is no bolt head anywhere on the outside of the frame.

Size	Groove it fits	Slot mouth	Bracket section	Typical use
M5 x 6	6.2 mm (20 series)	6 mm	30 x 21.2 x 8 mm	Light display and sign frames
M6 x 8	8.2 mm (30 series)	6 mm	30 x 21.2 x 8 mm	General enclosures and guards
M8 x 10	10.2 mm (40 series)	8 mm	30 x 21.2 x 8 mm	Machine frames with a visible face

Why the groove matters more than the thread. The thread size follows the groove, not the other way round. A 6.2 mm cavity will not take an M8 body, and an M5 body in a 10.2 mm groove would have nothing to wedge against. Match the size to the series before anything else.

The only joint that leaves no mark at all

Every other connector family in the range leaves some trace. A bracket is visible on two faces. A cubic connector is a visible block. A screw connector is hidden but needs a drilled core hole in the profile end. An end face connector is hidden but needs a tapped end face, which means the profile has to be cut, faced and threaded.

The inner bracket with top thread needs none of that. The profile ends stay square and closed, the faces stay untouched, and the only operation is the set screw going in from the groove. On a display frame, a door frame, a reception counter or any structure where all four faces are seen, it is the only joint in the range that produces a genuinely seamless corner.

Fully hiddenNo bracket, no bolt head and no drilled end. The only visible item is the groove itself, which can be closed with a slot cover.

No profile machiningThe profile needs only a clean square cut. No facing, no tapping, no core hole drilling — which also means you can re-cut a member on site.

Adjustable during assemblyThe bracket can be positioned anywhere along the groove before the set screw is tightened, so the joint self-aligns as you build.

Reversible, with a caveatThe set screw can be backed off and the joint taken apart, but the screw leaves a small witness mark on the groove floor each time.

Where this joint is the wrong answer

Because the joint is a wedge rather than a positive mechanical lock, it has two clear limits and it is worth being honest about both.

First, it is not a tension joint. The bracket resists the two members being pushed together and resists shear, but a load that tries to pull the members apart acts to un-wedge the bracket rather than to seat it harder. Where a member hangs or is pulled, use an end face connector or an anchor connector instead, both of which put the load into a thread rather than into a wedge.

Second, it is not a joint to be re-tightened weekly. Each tightening of the set screw bites into the groove floor. Two or three assembly cycles are fine; a joint that is opened every week will eventually lose its seating and start to move. For a frame that has to come apart regularly, use a bracket.

Assembling a hidden joint

Cut the members square and deburr the groove The bracket slides along the groove, so a burr rolled over by the saw will stop it dead. Run a deburring tool along both slot mouths before assembly.
Slide the bracket into the groove of the first member Insert it from the end of the member before that end is closed by anything else. This is the step that has to be planned into the build sequence.
Bring the second member up and check the alignment Slide the second member onto the bracket and check that the faces are flush and square before tightening anything. The joint self-aligns only while it is loose.
Tighten the set screw firmly but not excessively The set screw bites into the groove floor. Firm contact plus a quarter turn is enough; over-tightening deforms the floor and reduces the grip on the next assembly.
Cover the groove if the frame is a visible one A slot cover closes the remaining open groove and finishes the frame. Leave the grooves that will take accessories open.

Frequently asked questions

Will the joint hold if the frame is knocked?

It resists shock well in compression and shear, because the wedge seats harder under load. It is weak in tension, so a frame that can be pulled apart should use end face connectors at the corners that see tension.

Can I use it at the mid-point of a member rather than at a corner?

Yes. The bracket sits anywhere along the groove, so it works as a T-joint in the middle of a member as well as a corner joint. That is one of its advantages over an end face connector.

Does it work on an anodised profile?

Yes. The wedge acts on the groove geometry rather than on bare metal, so anodising does not affect the joint. The set screw will mark the groove floor on an anodised profile slightly more visibly than on a mill finish.

How much load can one bracket take?

Send us the joint load and the series and we will confirm. As a rule, treat a hidden inner bracket as a light to medium duty joint: adequate for enclosures, guards and display frames, not for a machine base carrying a dynamic load.

Do you supply the set screws with the brackets?

Yes. Brackets are supplied with the matching set screws in stainless or zinc plated steel, bagged by size. Tell us the series and we will kit them for the frame.

Send the series and the joint load direction

Tell us which series you are building in and whether the joint will be pulled. We will confirm the bracket size, supply the set screws and quote the frame hardware as a kit.

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