The blade does the work. The engine only turns it. Fit the wrong blade and a capable machine feels underpowered, cuts badly and wears itself out fighting vegetation it was never set up for.
Here is what each type is for.
Nylon line head
Flexible line rather than metal. Cuts soft grass and light weed, does no damage on contact with walls, posts or tree bark, and is the safest head for working near people or property.
Use it for edges, boundaries, around trunks and in gardens. It will not touch woody material.
Two-tooth and three-tooth blades
Flat steel blades with two or three cutting points. These are general grass and weed blades — fast, cheap, easy to sharpen with a flat file, and the most commonly used blade on Indian farms.
Three-tooth gives a slightly smoother cut and better balance than two-tooth. Both handle grass, soft weed and light fodder cutting. Neither is intended for woody stems.
Four-tooth and eight-tooth blades
More teeth means more cuts per revolution and a cleaner finish in dense material. Eight-tooth blades handle tougher, stemmy weed and light brush that would stall a three-tooth blade.
These are the middle ground: heavier than a grass blade, lighter than a saw blade.
Circular saw blades
Blades with forty, sixty or eighty teeth, shaped like a saw. These cut woody stems, scrub and small saplings. They need a machine with enough power and a solid gearbox to drive them.
They are also the most dangerous blade type, because they generate strong blade thrust when a tooth catches. Never use one without a guard, and never on a machine the manufacturer has not approved for it.
Chisel and shredder blades
Heavy blades designed to shred rather than slice, used for clearing dense rough growth where finish does not matter. They are slower but very tolerant of abuse.
Fitting a blade correctly
Blade fitting causes more accidents than blade choice. Work through it carefully:
- Stop the engine and disconnect the spark plug cap. Never change a blade with the plug connected.
- Lock the shaft using the locking pin or hole provided so the head cannot turn.
- Remember the thread is usually left-handed on brush cutter blade nuts. Turning it the way you expect will tighten it further.
- Fit the blade the correct way up, seated flat on the inner flange with no gap. Printed markings normally face outwards.
- Refit the outer flange, cup and nut in the original order. Missing one component leaves the blade able to move.
- Tighten firmly, then remove the locking pin and spin the head by hand to check it runs true.
- Check the guard is fitted and undamaged before starting.
Sharpening and replacement
Two and three-tooth blades sharpen easily with a flat file. Keep the original angle, take the same number of strokes on every tooth so the blade stays balanced, and file from the same side each time. An unbalanced blade vibrates, and vibration damages the gearbox and the operator's hands.
Saw blades need a round file matched to the tooth gullet, or a proper sharpening service.
Replace a blade rather than sharpening it when you see any of these:
- A crack anywhere, however small. A cracked blade can break apart at speed.
- A missing or badly chipped tooth.
- Visible bending, or wobble when spun by hand.
- Teeth filed back so far the blade has lost its original profile.
A note on cost
Blades are consumables. Treating them as permanent fittings is how people end up running a bent, blunt blade that makes the machine vibrate, burns extra fuel and cuts badly. Keeping two or three spares of the type you use most is cheap insurance — see brush cutter spare parts, or the full brush cutter range if you are choosing a machine.