Self-Tapping Screw Connector for Aluminium Profile M6 M8 M10 to 50 mm Series

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

A self-tapping screw connector for aluminium profiles in M6, M8 and M10. Forms its own thread in the profile core bore for a completely hidden joint with no visible fixing.

Wholesale Price $0.09 - $0.42 / pc per pc

Material	Hardened steel, zinc plated or stainless
Alloy Grade	Hardened carbon steel, zinc plated; 304 stainless option
Temper	custom
Section Size	M6, M8 and M10 studs to suit profile core bores
Slot	Fits the core bore of 30, 40, 45 and 50 series profiles
Length	Stocked in standard lengths, custom lengths on request
Tolerance	ISO 965-2 thread tolerance 6g
Surface	Zinc plated or stainless, passivated
MOQ	1000
Lead Time	12-20 days after deposit
Loading Port	Shanghai / Ningbo
Supply Ability	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 · Threaded joints

A screw connector for aluminium profile is a hardened steel stud with a flange head that is driven into the core bore at the end of a profile and forms its own thread in the aluminium. It is made in M6, M8 and M10 and is the cheapest way to hide a joint completely: no bracket, no bolt head, no visible fixing of any kind. The stud goes into one member’s end, the second member is brought up over it, and a cross bolt through the second member locks the joint.

The one thing that decides whether this joint works or fails is the size of the hole you drill. A thread-forming screw does not cut the aluminium away, it displaces it, so the core hole has to be larger than the tapping drill you would use for a cutting tap. Drill the cutting size and the screw will seize; drill too large and it will strip. The exact figures are in the table below, and they are not the ones most people expect.

The screw connector: a hardened flanged stud that forms its own thread in the profile core bore.

Forming a thread is not the same as cutting one

A cutting tap removes metal to create a thread. A thread-forming screw does the opposite: it pushes the aluminium aside, so the material that ends up forming the thread flanks is cold worked and slightly harder than the parent metal. In a soft alloy like 6063 that is an advantage — the formed thread is stronger than a cut one of the same size, and there is no swarf to clear from a blind hole.

The consequence is that the core hole is bigger, not smaller, than a tapping drill. For an M8 x 1.25 thread a cutting tap needs a 6.8 mm hole; a thread-forming screw needs about 7.4 mm. Drill 6.8 mm for a forming screw and it will jam and shear; drill 8.0 mm and there will not be enough material left to form a thread.

Thread	Pitch	Cutting tap drill	Thread-forming core hole	Difference
M6 x 1.0	1.0 mm	5.0 mm	approx. 5.5 mm	+0.5 mm
M8 x 1.25	1.25 mm	6.8 mm	approx. 7.4 mm	+0.6 mm
M10 x 1.5	1.5 mm	8.5 mm	approx. 9.2 mm	+0.7 mm

Use the forming hole, not the tapping drill. This is the single most common cause of a failed screw connector installation. The two holes differ by half a millimetre, which is nothing until the screw seizes halfway in with no way to back it out.

Engagement decides the strength

A thread in aluminium needs more engagement than the same thread in steel, because the aluminium is what shears. The working rule is one diameter of engagement as an absolute minimum and one and a half diameters for full strength. Below one diameter the thread strips before the bolt breaks; above one and a half diameters extra depth adds nothing.

Thread	Minimum engagement (1 x d)	Full strength (1.5 x d)	Torque ceiling in aluminium
M6 x 1.0	6 mm	9 mm	approx. 8 N m
M8 x 1.25	8 mm	12 mm	approx. 15 N m
M10 x 1.5	10 mm	15 mm	approx. 28 N m

Compare those torque figures with what the same bolt would take in a steel thread — about 10 N m for M6, 25 N m for M8 and 49 N m for M10 — and you can see that the joint is limited by the aluminium, not by the fastener. Torque a screw connector to its steel value and it will strip the formed thread out of the profile.

The cheapest hidden joint, and the least re-usable

Every time the joint is taken apart and re-made, the forming screw removes a small amount of material from the thread it created. The first assembly is strong, the second is nearly as good, and by the fifth the thread is loose. That behaviour is inherent to the design and no amount of care changes it.

Assembly cycle	Thread condition	What to do
First assembly	Full formed thread, full torque	Torque to the ceiling in the table above
Second and third	Thread still sound, slight loss of grip	Reduce torque by about 20 per cent
Fourth and fifth	Thread visibly worn, joint may creep	Acceptable for a light non-structural joint only
Beyond five	Thread stripped or loose	Re-drill oversize and use a threaded insert, or move to a new joint type

The practical conclusion is that a screw connector belongs on a frame that is assembled once and then left alone — a production machine, a fixed guard, a conveyor frame that will not be modified. It does not belong on a prototype, on a frame that will be re-configured, or on a joint that has to be re-torqued during commissioning. For those, use an end face connector or a bracket, both of which can be taken apart indefinitely.

Installing a screw connector

Drill the core hole to the forming size, not the tapping size Use the middle column of the first table. Drill the hole square to the end face and deburr the mouth.
Drive the stud in one continuous pass A forming screw should go in without stopping. Stopping and restarting damages the thread that has already been formed.
Stop when the flange seats on the end face The flange is the depth stop. If it will not seat, the hole is undersize and forcing it will shear the stud.
Bring the second member over the stud and fit the cross bolt Check the joint is square before tightening the cross bolt, because once it is tight the position is fixed.
Torque to the aluminium ceiling Use the torque figure from the table, not the bolt’s steel rating. The aluminium thread is what fails.

Frequently asked questions

Can I use an ordinary bolt instead of a screw connector?

No. A standard bolt needs a pre-cut thread, and drilling and tapping a deep core hole in a long profile is not practical on site. The screw connector exists precisely so that the thread can be formed at assembly.

Will it work on an anodised profile?

Yes. The forming screw cuts through the anodised layer at the bore, which is a few tens of microns thick. It does mean the thread is formed in bare metal and is not protected from corrosion, so use it indoors or add a sealing compound in wet environments.

What happens if the thread strips?

Re-drill the bore oversize and fit a threaded insert, which gives you a steel thread and a joint that can be dismantled many times. That is the standard repair and it leaves the member usable.

Which size should I choose?

Match the stud to the profile’s core bore. Use M6 for 30 series, M8 for 40 series and M10 for 45 and 50 series. Going larger than the core bore allows is not possible; going smaller wastes capacity.

Do you supply the studs with the drill size marked?

Yes. Studs are bagged by size with the forming core hole diameter and the torque ceiling printed on the label, so the installation data travels with the parts.

Send the series and how often the joint is opened

Tell us the profile series and whether the frame will be re-configured. We will confirm the stud size and core hole, and supply the forming data with the parts.

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