Carbon fiber rods don't get as much attention as tubes, but honestly, they're just as useful. I've seen them used for everything from RC airplane wing joiners to robotic arm linkages to kite spars. If you're not familiar with what's available, it's easy to pick the wrong size or type.

Here's what I've learned from handling these things day in and day out.

Solid Rod vs Tube: When to Use Which

The simple rule: use a rod when you need a solid cross-section for strength in a small diameter, or when you need to fit something inside a tube. Use a tube when you need to save weight. A 6mm solid rod is way stronger than a 6mm tube, but it's also heavier. For most structural applications where weight isn't critical, a rod is fine. For long spans or weight-sensitive builds, go with a tube.

Pultruded Carbon Fiber Rods

Most of our carbon fiber rods are pultruded — continuous unidirectional fibers running the full length. This makes them incredibly stiff along the axis but more brittle if bent sideways. If you're using a rod as a wing joiner in an RC plane, that unidirectional stiffness is exactly what you want. The loads run along the rod, not across it.

Our carbon fiber rods range from 1mm up to 20mm in diameter and come in 500mm lengths. The 1mm and 1.5mm rods are popular for small control linkages and pushrods in micro RC planes. The 3mm and 4mm sizes are common for quadcopter arms on smaller builds. The bigger ones — 8mm, 10mm, 12mm — are usually used for structural spars or heavy-duty applications.

Stiffness by Diameter

Here's something a lot of people get wrong: stiffness doesn't scale linearly with diameter. It scales to the fourth power (for bending stiffness). That means going from 3mm to 4mm — just a 1mm increase — gives you roughly three times the stiffness. A 6mm rod is about 16 times stiffer than a 3mm rod of the same material.

I mention this because I see people choosing way oversized rods thinking they need the extra size, when a modest step up in diameter would already give them more than enough stiffness with less weight.

Cutting and Working With Rods

Carbon fiber rods are easier to work with than tubes in some ways — no worry about crushing a hollow cross-section. A fine-tooth hacksaw or a Dremel with a cut-off wheel works well. Sand the cut end lightly to smooth any splinters.

One thing to watch: the dust is conductive and itchy. Wear gloves and a mask. Don't blow the dust around with compressed air — vacuum it up instead.

Common Applications

• 1-2mm: RC control rods, pushrods, small kite frames
• 3-4mm: Small drone arms, RC plane wing joiners, 3D printer frame supports
• 5-6mm: Medium RC planes, camera rig supports, tent poles
• 8-10mm: Large RC models, structural supports, robotic arms
• 12-20mm: Heavy industrial applications, custom engineering

Bottom Line

Carbon fiber rods are simple, strong, and surprisingly affordable. If you're building something that needs a straight, stiff structural member and weight matters, they're hard to beat.