Which Tube Clamp Fitting Do You Need? Start With the Size

Pick the diameter before you pick the shape. We stock tube clamp fittings in two sizes, Ø27 mm and Ø42 mm, and more than half the range exists in only one of them. Choose the size first and the build goes together in an afternoon. Choose the shape first, fall in love with a fitting that only comes in Ø42, and you'll be repacking a box.

This is the call we get most often on the phone: someone has a pile of tube in one size and a basket of fittings in the other. So here's the whole system laid out, including which of our 19 fittings come in which diameter, and what each one is actually for.

Measure the tube, not the hole

Tube clamp fittings clamp onto the outside of a tube. That means the number that matters is the outside diameter of your tube, not the bore, not the wall thickness, and definitely not what the old invoice said. Put a caliper or a tape across the end of the tube and read the outside face to outside face.

Our two sizes line up with the standard steel tube diameters the trade uses across Europe. Ø27 mm is the 26.9 mm outside diameter tube, sold as 3/4" nominal bore, and known in the UK as A tube or size 5. Ø42 mm is the 42.4 mm tube, 1 1/4" nominal bore, the one UK suppliers call C tube or size 7. If you're cross-shopping a British key clamp catalogue, those are the codes to match. And if your tube came from somewhere else, measure it anyway before ordering.

Ø27 or Ø42: which one is your build?

Ø27 is the lighter system. It's the right pick for clothes rails, shelving, market stalls, display frames, garden structures, desk and table legs, and anything where the frame is doing a job but nobody is going to lean their bodyweight on it. It's cheaper per metre and it looks less industrial, which for furniture is usually the point.

Ø42 is the structural one. Handrails, guardrails, barriers, workshop racking, mezzanine edge protection, anything people will grab, lean on, or fall against. It's also the size with the deeper fitting range, so if your design needs an unusual junction, Ø42 is more likely to have it.

A rough cost check from our own price list, so you can budget before you design: a 3-metre Ø42 tube in black is €39.19, while a 300 mm Ø27 galvanised offcut is €2.79. Fittings sit between €2.90 and €5.67 across the whole range. Tube length is what moves the total, not the fittings.

Which fittings come in which size

This is the table we wish every supplier published. Nine of our fittings are Ø42 only, four are Ø27 only, and six come in both.

Read that table before you draw your design, not after. The Ø27-only cluster is telling you something: the swivels, the wall plate and the lugged bracket are furniture and light-frame parts. The Ø42-only cluster is handrail and roof-frame parts. The system is built around what each size is realistically asked to do.

What the fittings actually do

Elbows and corners are the easy ones. A 90° elbow turns a corner in one plane. A 3 way corner elbow does the top corner of a box, where three tubes meet at right angles in three directions. If you're building anything cuboid, you'll need four of those.

Tees are where people over-order. A short tee lets a tube run continuously through the fitting while a second tube branches off at 90°. The long tee does the same job with a longer clamping sleeve on the through tube, which matters when the through tube is carrying load and you want the grip spread further. A 3 way outlet tee adds a leg out of the plane.

Then there's the pair that gets confused constantly. A two socket cross clamps both tubes where they cross, in the same plane. An offset crossover carries one tube past the other with a step in it, so they cross without fighting for the same space. Different problems, similar-looking parts.

Base flanges, wall plates and lugged brackets are how the frame meets the building. A base flange stands an upright on a floor and takes the fixings. A wall plate does the same against a vertical surface. The wall mount handrail bracket is the one you want if a rail runs along a wall rather than standing free.

Swivels handle everything that isn't a right angle. Stair rails, raked braces, ramp handrails. In Ø27 they come as a male and female pair that you buy together; in Ø42 the double inline swivel combination gives you two adjustable joints in one body, which is the dearest fitting we sell at €5.67 and worth it when the alternative is cutting compound angles.

Tube clamps are not scaffold couplers

Worth being blunt about, because it's an expensive mix-up. Scaffold tube is Ø48.3 mm. Our tube clamp fittings top out at Ø42 mm, so they will not fit scaffold tube, and a scaffold coupler will not grip Ø42 tube properly either. Two different systems that look related in photographs.

If you're working with real scaffold tube, you want scaffolding couplers instead, which are a different shape, a different standard, and rated for a different job. If you're building furniture, railings or frames from Ø27 or Ø42 tube, you're in the right place with tube clamp fittings.

Black or galvanised

Nearly everything in the range comes both ways, at close to the same price. The Ø42 elbow is €4.20 galvanised and €4.44 in black, so cost isn't going to decide it for you.

Galvanised for anything outdoors or damp: garden frames, carports, external handrails, anywhere with rain or condensation. Black for indoor work where the look matters, which is most furniture, shop fitting and clothes rails. Black is a coating rather than a sacrificial layer, so a scratch in it outdoors will start rusting where a scratch in galvanising largely won't.

Tightening them

Every fitting is held by grub screws that you drive with an Allen key. No welding, no drilling the tube, no specialist tools. The screw tip bites into the tube wall and that bite is what carries the load, which is why the tube has to be clean and free of paint or heavy scale under the fitting.

The major key clamp manufacturers publish 39 Nm as the tightening figure for their fittings, giving roughly 900 kg of axial slip resistance per screw. We don't publish a tested slip load for our range, so treat that number as the industry reference point rather than a promise about our parts. Tighten firmly with a proper Allen key, check the screws again after the first week of use, and don't design a fall-protection guardrail off the back of a blog post. That one needs an engineer.

Common questions

Can I mix Ø27 and Ø42 in one structure?

Only by keeping them in separate runs, because no fitting bridges the two sizes. People do it deliberately, say Ø42 uprights with Ø27 infill, but every junction between the sizes needs a bolted plate or a bracket rather than a clamp.

Do I need to cut the tube exactly?

For tees, crossovers and anything the tube passes through, no, length is forgiving. For elbows and butt joints where two cut ends meet inside a fitting, yes, a few millimetres shows. We sell steel tube cut to eight fixed lengths from 300 mm to 3000 mm, which saves most people a cutting job.

Can I take it apart later?

Yes, and that's the main reason to build this way. Back the grub screws off and the frame comes apart. The tube keeps the screw dimples, so a fitting reused in the same spot will re-seat happily, though it's worth rotating the tube slightly if you're clamping in a fresh position.

How many fittings will I need?

Count your junctions, not your tubes. A simple rectangular frame standing on the floor is four corners, four base flanges, and a tee for every mid rail. Add ten percent, because everyone finds one junction they didn't draw.

Start with the size

If you take one thing away: settle on Ø27 or Ø42 before you add anything to a basket, and check the table above against your design. Our full tube clamp fitting range lists the available sizes on every product page, and if you want to see the system built into something real first, our guide to building a handrail with tube clamps walks through an actual half-hour job.

Still not sure which size your tube is? Send us a photo of a tape measure across the end of it. We'd rather answer that email than process your return.