Nylon string heads handle grass, edges, and light weeds, while rigid metal blades take down dense brush — and each attachment carries its own safety rules.
Fitting the wrong cutting attachment to a trimmer turns a routine yard job into a hazard. STIHL’s trimmer and brushcutter safety manual splits the work cleanly: flexible line for grass, lawn edges, fences, tree surrounds, and light weeds; a rigid metal blade for dense, tall, woody, or brushy growth that would shred line in seconds. Switching to metal also switches the equipment you need, the hazards you face, and the clearance your model must have from the manufacturer.
What Each Attachment Is Actually For
Match the attachment to the vegetation, not to what fits on the shaft. Nylon line is flexible, so it forgives contact with fencing, siding, and tree trunks instead of gouging them. A steel blade is rigid and cuts aggressively through woody stems that would stall a string head.
- String head: grass, lawn edges, fence lines, tree surrounds, and light weeds. Use only the specified nylon line at the intended length — the line-limiting blade in the properly installed deflector trims the excess automatically.
- Metal blade: dense, tall, woody, or brushy vegetation. Rigid steel blades are meant for grass, brush, and similar growth — not for stony ground.
Where Metal Blades Become Dangerous
A blade that strikes a rock, fence post, or hard object can crack, chip, break, or throw fragments, and it can spark. Never run a metal blade near stones, masonry, fencing, buildings, or tree trunks, and never where wildfire or flammable-material risk exists. Blades kick out and damage easily in stony areas, which is why string heads stay the safer choice along planted beds and structures. Metal blades also demand heavier personal protection: inspect the blade before every use, keep it sharp, and stop immediately if it’s cracked, chipped, bent, dull, or poorly secured.
| Attachment | Best Use | Key Limits |
|---|---|---|
| Nylon string head | Grass, lawn edges, fences, tree surrounds, light weeds | Specified nylon line only; no wire or metal-reinforced line |
| Metal blade | Dense, tall, woody, brushy vegetation | Not for stony areas, fences, buildings, or tree trunks |
| Deflector with line-limiting blade | Required on any trimmer or brushcutter running a mowing head | Must be the correct, properly installed guard |
| Handle and harness | Blade work requires the manufacturer-specified handle and harness | Line-head setup is not enough for blade use |
| Personal protection | Eye protection and protective clothing for all cutting | Heavy-duty gloves required when handling a blade |
| Bystander clearance | Applies to every attachment type | |
| Transport | Cover metal blades with a transport guard; shut the machine off before setting it down | Never carry the machine with the attachment moving |
Will A Metal Blade Fit Your Trimmer?
Only if the manufacturer says so for your exact model. Cutting attachments are not universally interchangeable — a shaft attachment that slides on is not proof of compatibility. Use only attachments specifically authorized for your model, and match the unit with the correct deflector, handle, and harness. The checklist runs through battery voltage, shaft interface, guard, rotation direction, and the model’s approved attachment list in the manual. “Universal” marketing language does not establish compatibility. This applies across gasoline, corded, and battery powerheads, plus dedicated brushcutters, and only where the maker expressly supports the attachment.
If you’re shopping for a unit factory-cleared for blade work, this roundup of a cordless brush cutter with metal blade covers models built for it. For the official rules, Stihl’s trimmer and brushcutter safety manual is the document to read before you swap heads.
The Mistakes That Cause Most Blade Injuries
Most metal-blade accidents trace back to a familiar handful of shortcuts. Fitting a blade to a model that isn’t approved for it tops the list, followed by keeping a line-head guard or harness in place when the blade calls for different equipment. Running a blade near rocks, fencing, masonry, tree trunks, or dry brush invites kickout and sparks. Other frequent errors: using line that’s too long, wire line, metal-reinforced line, or improvised cutting media; continuing with a cracked, chipped, bent, or dull blade; and cleaning a jammed head while the engine runs or the battery stays connected. Stop the engine or disconnect power and wait for the attachment to stop before installing, removing, cleaning, or servicing it, and operate at ground level with the attachment parallel to the ground, since above-ground or perpendicular use raises injury risk.
Common Questions
Can I put a metal blade on any string trimmer?
No. Only models the manufacturer expressly approves for blade attachments can run them, and you must fit the specified deflector, handle, and harness. A blade that physically mounts on the shaft is not proof of compatibility. Check your model’s manual and its approved attachment list before buying a blade.
Is a string head safer than a metal blade?
For most residential work, yes. Nylon line is flexible and less likely to damage fencing, siding, or tree bark, and it doesn’t spark or throw steel fragments. Metal blades cut more aggressively but add kickback and breakage hazards, so they belong in dense or woody growth away from hard objects.
What line can I use in a string head?
Only the nylon line specified for your machine, cut to the intended length. Never substitute wire, metal-reinforced line, or improvised material. The line-limiting blade inside a correctly installed deflector trims excess line down as you work, which is why the right guard matters.
Sources
- STIHL USA. “Trimmer and Brushcutter Safety Manual.” Source for attachment selection, metal blade hazards, installation rules, and the 50-foot bystander clearance.