Carbon Fiber Telescoping Tubes: Getting the Clearance Right
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The only thing that matters
Forget stiffness for a minute. When you're building something that telescopes, one number decides whether it works: the gap between the inner tube's outside diameter and the outer tube's bore.
Get that right and everything else follows. Get it wrong and you have either a joint that rattles and wobbles, or a joint that won't move at all — and carbon on carbon is unforgiving in that second direction, because it doesn't have the give that metal does.
So this is a piece about clearances, and about which sizes in our catalogue actually nest inside each other.
What the numbers look like
A telescoping joint has three dimensions that matter.
The outer tube's bore. That's the hole the inner tube slides into.
The inner tube's outside diameter. That's the part doing the sliding.
The gap between them. Subtract one from the other and that's your total clearance, spread around the circumference.
Here's the useful part: at the sizes people actually build with, a 1mm total gap — half a millimetre per side — is the figure that works. It's small enough that the joint doesn't rattle noticeably, and large enough that the inner tube moves without binding when you're holding it slightly off-axis.
Which means you can work out nestings straight from our catalogue:
| Outer tube | Its bore | Inner tube that fits | Total clearance |
|---|---|---|---|
| 22 × 19mm | 19mm | 18mm | 1mm |
| 20 × 19mm | 19mm | 18mm | 1mm |
| 25 × 23mm | 23mm | 22mm | 1mm |
| 16 × 12mm | 12mm | 11mm | 1mm |
| 14 × 10mm | 10mm | 9mm | 1mm |
| 12 × 8mm | 8mm | 8mm | 0mm — binding |
That last row is the one to watch. A 12mm tube with an 8mm bore does not take an 8mm tube, not even close. Eight into eight is interference, and you'll find that out by jamming it, not by it sliding in. Always check the bore, never the outside diameter of the size "next to" the one you have.
Carbon on carbon binds. This is not a maybe.
This is the part that catches people who are used to metal telescoping sections.
Aluminium on aluminium will gall a little and then wear itself a clearance and keep working, badly. Carbon on carbon does something different: the two surfaces are the same hardness, they're both abrasive, and there's no lubrication happening. Push a carbon tube into a carbon bore and you're sanding both faces against each other, shedding dust into the joint, and progressively increasing the clearance in the worst way — unevenly.
Two things to do about it.
Increase the clearance slightly. If you're building a joint you'll move often, go to 1.5mm total rather than 1mm. It'll feel loose when you first assemble it. It'll feel right after a season of use.
Put something in between. A nylon or aluminium liner sleeve, a thin wrapping of PTFE tape on the inner tube, or an aluminium section at the joint rather than carbon. Any of these stops the two carbon surfaces from touching, and any of them will roughly double the working life of the joint.
There's also a galvanic consideration if you introduce aluminium. Carbon and aluminium in contact with moisture corrodes the aluminium, which is covered in more detail in our carbon fiber and aluminium comparison. A liner is still the right answer — just be aware of the pairing.
Locking it
A clearance fit slides. It does not hold. You need something that clamps.
A tube clamp is the simplest answer and the one we'd recommend first. Slacken it, slide, tighten it. Our own clamps run from 10mm to 40mm and work directly on the outer tube. The advantage over a twist-lock is that it's visible: you can see whether it's tight, and you can see whether it's come loose.
A compression collar is tidier and works on the same principle. Slightly more expensive, slightly less inspectable.
Friction alone works surprisingly well if the clearance is small and the load is light, and it's what most cheap telescoping poles rely on. It also fails without warning, which is why we don't recommend it for anything critical.
Whatever you use, add a sleeve inside the inner tube at the clamping point if the wall is thin. A clamp squeezing a 0.5mm wall will crush it — that's what our reinforced sleeves are for.
Stiffness at the joint is the real penalty
Worth saying plainly, because it's the thing people underestimate.
A telescoping section is much less stiff than a solid one. Not slightly — substantially. Three reasons stack up: the inner tube is a smaller diameter than the outer, the joint can't transmit bending moment through a clamped connection the way a continuous tube can, and the jointed length has effectively no support between the clamp and the end.
Practically, that means a telescoping assembly should be designed for the extended length, not the retracted one. If your pole is 1.5m extended and you've sized the tube for a 1.5m continuous span, it will feel much worse than you expect. Size it as though the joint is a hinge and the only thing holding it straight is the clamp — which is close to the truth.
The fix is either more diameter at the joint, or more overlap. Overlap is the cheaper one: if the sections overlap by three diameters rather than one, the joint behaves much closer to solid, because you've given the clamp something to resist.
Keeping the inside clean
One maintenance point, and it matters more with carbon than with metal.
Dust and grit inside a telescoping joint are abrasive, and on carbon they do real damage rather than just making it gritty. Wipe the inner tube before you assemble, and if the joint is going to be used in sand or on a beach, fit end caps on the open ends so the cavity stays sealed. Our tube caps cover 10mm to 62mm.
Don't lubricate a carbon-on-carbon joint with oil or grease. It attracts grit and turns the joint into a grinding paste. If you need something, a dry PTFE spray is the better choice, and a liner is better still.
What we'd build, in practice
For a light tripod or antenna mast, we'd use a 22 × 19mm outer with an 18mm inner. That's a 1mm gap, a clamp at the joint, and a sleeve inside the 18mm where the clamp bears. It'll be light, it'll slide, and it'll need occasional wiping rather than maintenance.
For something that gets moved daily, we'd go up a wall on the outer so the clamp doesn't mark it, and add a nylon liner at the joint.
For a heavy load or a long extension, we'd stop trying to make it telescoping in carbon alone and use an aluminium inner section. Metal takes the abrasion better, and the galvanic risk is manageable with isolation. It costs weight where you can most afford it — at the inner end, already close to the centre.
Frequently asked
What clearance should a telescoping carbon fiber tube have?
About 1mm total for a joint you assemble occasionally, and 1.5mm for one you move often. That's 0.5 to 0.75mm per side. Tighter than that and carbon on carbon will bind rather than slide.
Will a carbon tube slide inside another carbon tube?
It will, and it will wear as it does. The two surfaces are the same hardness, so they abrade each other and shed dust into the joint. A nylon or aluminium liner at the sliding interface roughly doubles the working life — and it's the single best thing you can do for a telescoping build.
How do I work out which sizes nest?
Take the outer tube's bore from its product page and subtract the inner tube's outside diameter from it. Our sizes are listed as outside diameter × bore, so a 22 × 19mm outer has a 19mm bore and takes an 18mm inner with 1mm of clearance.
Why does my telescoping joint flex so much?
Because a clamped joint doesn't transmit bending moment like a continuous tube, and the inner section is a smaller diameter than the outer. Size the assembly for its extended length and increase the overlap between sections — three diameters of overlap is the point at which the joint starts behaving closer to solid.
Can I lubricate it?
Not with oil or grease, which attracts grit and turns the joint into a grinding paste. A dry PTFE spray is acceptable. A liner is the better answer.
Tubes are grouped by outside diameter in the carbon fiber tube sections, and the bore options are on each product page. Clamps, caps and sleeves are in tube parts. If you're sizing a joint, tell us the outer tube and the extension length and we'll work out the inner size for you.