Short answer
Cutting capacity is the thickest branch a trimmer is designed to cut, and it is largely set by the gap between the blade teeth. Manufacturers quote a figure in millimetres; real-world performance depends on blade sharpness, motor power and how woody the growth is.
What the numbers mean
A wider tooth gap lets thicker stems enter the blade, but does not guarantee a clean cut: stems that are too hard can stall the blade. Treat the quoted capacity as a ceiling, and use loppers or a pruning saw above it.
Tips
- Compare tooth gap and blade speed, not just power.
- Keep blades sharp: see sharpening.
- For thick stems, see trimmers for thick branches.
- If a stem stalls the blade, stop, isolate power and cut it by hand.