Carbon Fiber Tube Sizes Explained: How to Choose OD, ID and Length

So you need a carbon fiber tube.

First question I'd ask you: 10mm outside, or 10mm inside? Because that's usually where it goes sideways. Someone writes "10mm tube" meaning the hole. Someone else writes "10mm tube" meaning the outside. Both think they've been clear. Neither is.

Here's what that costs you. A 10mm tube in our range comes with a 6mm bore, an 8mm bore, or a 9mm bore. Three products. One label. The 10x6 runs about three times as stiff as the 10x9 — same outside diameter, same look in a photo, and they will behave completely differently in the same frame. That's the whole problem in one example.

Three numbers solve it. Outside diameter, bore, length. Wall you don't get told and don't need telling, because it falls straight out of the other two.

Outside diameter (OD) is your fit

Measure across the tube. Outside of one wall to outside of the other. That's OD.

Whatever the tube slides into is sized off this number. A clamp, a cap, a sleeve, a drilled hole in a frame plate. Sixteen millimetre clamp, sixteen millimetre tube. No wiggle room, and no bore on earth rescues a tube that's the wrong OD for the fitting you already own. I've watched people try. They send it back.

OD does the heavy lifting on stiffness too, and more than most people expect. Same wall, double the diameter, and you get roughly eight times the stiffness. Eight. That's why drone arms are fat and short instead of thin and long — the diameter is doing the work, not the wall.

We stock 5mm through 200mm. Under 25mm it's mostly model aircraft. Past 40mm you're in mast and boom territory, telescoping sections, industrial frames, the odd bit of structural repair work.

Bore (ID) — this is the one people get wrong

The hole down the middle.

Same outside, different bore, different product. We list an 8x4mm and an 8x6mm square tube. Identical outside. One's got a 2mm wall, the other's got 1mm. Pick blind and you get either something heavier than your design needs or something that flexes more than you planned for. Neither one announces itself until the build is done.

Wider bore, bigger hole. Handy when you're threading a shaft through, or a thinner tube, or a run of wire. Costs you wall. That's the trade, and it's the only trade there is.

Wall thickness is the number you can actually feel

You won't find it printed on many listings. Ours included, mostly, because it isn't a measurement — it's arithmetic.

Wall = (OD − bore) ÷ 2

10mm with a 6mm bore: 2mm wall. 10mm with a 9mm bore: 0.5mm. Both sold as 10mm tube.

When a customer tells me a tube "feels flimsy", nine times out of ten they're describing thin wall, not small diameter. When they say it feels dead, heavy, overbuilt — thick wall. Stiffness climbs fast with wall. Weight climbs with it. Usually the right answer is the thinnest wall that still carries what you're putting on it, and no thinner. There is a fuller treatment of which wall suits which diameter in the wall thickness guide.

One warning before you go thin. Thin walls dent. Put a clamp on a 0.5mm wall, do the bolts up properly, and you'll crush the tube flat at that point. This is exactly what reinforced sleeves exist for — aluminium insert pushed into the end, so the clamp squeezes metal instead of carbon.

Sizes we actually sell, and what each one is for

Outside	Bore	Wall	What it's usually for
5mm	3mm	1mm	Small models. Stiff for its size
6mm	4mm	1mm	Same idea, a touch more
8mm	6mm	1mm	Light duty, short spans
8mm	4mm	2mm	Twice the wall of the 8x6. Noticeably stiffer
10mm	6mm	2mm	The workhorse
10mm	8mm	1mm	Half the wall of the 10x6
10mm	9mm	0.5mm	Very light. Dents. Sleeve it if you're clamping
12mm	8mm	2mm	Arm stock
16mm	12mm	2mm	Bigger airframes
20mm	16mm	2mm	Structural. Booms, spars, load-bearing
20mm	19mm	0.5mm	Thin shell. Cosmetic, or weight-critical

Read the last column rather than the first. That's the pattern — bore isn't a footnote, it's the difference between two tubes that share a size label and behave like different materials.

Length, and the thing nobody warns you about

500mm and 1000mm. That's what we stock as standard.

Long tubes bend more than short ones. Obvious when you say it out loud, less obvious when you've got a tube that felt rigid at 200mm and you span 600mm with it and watch it sag. Going up a diameter fixes that better than going up a wall. Counter-intuitive, but it's where the stiffness lives.

The other thing is shipping. Past a certain length, carriers get awkward and freight jumps — a 1000mm tube can cost you disproportionately more to send than two 500mm ones. If your design can live with a joint, sometimes it should.

What to buy for what

Model aircraft are a large share of what we ship, and they follow their own logic — spars want a large diameter at a thin wall, pushrods want pultruded rather than roll wrapped. There is a guide to that specifically.

Straight from WHABEST's own order history, roughly grouped. If you want the full numbers — which single spec accounts for a fifth of everything we ship — that is broken down in our order data write-up.

Drone and multirotor arms: 16mm to 25mm outside, 2mm wall, roll wrapped 3K, plain weave, matte. Stiff wins, arms are short, weight is tolerable.

Small fixed-wing and gliders: 5mm to 10mm outside, 1mm wall. Here light beats stiff and it isn't close. The 8x6mm is the one that moves.

Kite spars: thin walls, small diameters, 5x3 and 6x4. These are meant to flex and spring back — the thin-wall versions aren't a cheap substitute, they're correct.

Pushrods and linkages: usually pultruded rather than roll wrapped. Smoother surface, cheaper at these diameters, stiff down the length. That's a pushrod.

Robot frames, camera sliders, jigs: 20mm and up, generous wall, bolted through clamps. Plan for sleeves at the fixing points before you drill anything.

Telescoping anything: bore is the whole game. Inner tube has to be just under the outer tube's bore. Carbon on carbon will bind — you want clearance, and probably a liner.

The two we get every week

Buying on outside diameter alone. Listing says "20mm carbon fiber tube", buyer assumes there's one of them. There are usually four or five bores under that size. The dropdown is right there.

And the second: assuming the bore is about half the outside. Sometimes it is. We also list 20x14 and 20x19. Split the difference from "about half" and you've ordered neither, which you discover when the box arrives.

Stuck? Send the OD you need and what the tube has to do. I'll suggest a bore. One email versus one return.

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Frequently asked

OD and ID — which do I order by?

OD when you're matching something the tube goes into: clamp, cap, sleeve, drilled hole. ID when you're matching something that goes into the tube. If both apply, get the bore right first and size the outside around it.

How do I measure one I already own?

Calipers across the outside for OD, then the hole for ID. Subtract, halve, that's your wall. Measure the OD in two places on anything small and take the lower reading — a tube off the mandrel can come out slightly oval, and the small number is the one that decides whether it fits.

Thicker wall, stronger, right?

Stiffer for the same diameter, yes. Heavier, also yes, and past a point you're paying for material that isn't doing much work. Thin walls dent more readily. Better question: what's the thinnest wall that carries my load? The span and the weight normally answer it.

Bigger bore = weaker tube?

Same outside diameter, yes. You've moved material away from the wall, so both stiffness and crush resistance drop. Want the hole and the stiffness? Bigger outside diameter. Not a thicker wall.

Can I cut these myself?

Almost everyone does. Fine-tooth blade or abrasive disc, slow, and support both sides of the cut or the wall pinches shut. Mask on. Carbon dust isn't something you want in your lungs.

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Sizes are grouped by outside diameter in the tube sections. If you are sizing a drone arm rather than picking a general-purpose tube, the drone arm guide works from arm length to diameter, and cutting it is covered in the workshop guide. Buying in bulk, the wholesale listings do 10 and 20 piece packs. Size not there? Ask. Custom diameters and lengths usually aren't a problem.