Last Updated: March 29, 2026
String Trimmer Line Types Guide: Shape, Size, and Which to Buy
String trimmer line comes in dozens of shapes and diameters ā and the right choice depends on your trimmer’s power class, the types of vegetation you’re cutting, and whether you prioritize cutting efficiency or line longevity. This guide covers every line type, explains what the shape differences actually mean for performance, and helps you choose the right replacement line for your trimmer.
String Trimmer Line Sizes by Application
| Diameter | Duty Class | Best For | Typical Trimmer |
|---|---|---|---|
| 0.065″ | Light | Thin grass, light weeds, small residential trimmers | Cordless 20Vā40V, small corded |
| 0.080″ | Light-medium | Standard residential lawn trimming, light edging | Most cordless 40V+, light gas |
| 0.085″ | Medium | All-around residential use, light brush | Mid-range gas and cordless |
| 0.095″ | Medium-heavy | Dense grass, heavier weeds, edging | Standard gas trimmers |
| 0.105″ | Heavy | Dense weeds, thick grass, light woody stems | Commercial-grade gas trimmers |
| 0.110″ā0.130″ | Extra heavy | Brush, heavy weeds, commercial use | High-power commercial trimmers only |
Caution: Using line that’s too thick for your trimmer’s power class will bog down the motor, reduce RPM, and wear out the engine or motor faster. Always check the manufacturer’s recommended diameter range in your trimmer’s manual.
String Trimmer Line Shapes Explained
| Shape | How It Cuts | Best For | Durability |
|---|---|---|---|
| Round (circular) | Smooth, consistent cut arc | General grass trimming, easiest on trimmer | Good longevity ā smooth profile resists breakage |
| Square | Sharp corners cut aggressively | Dense grass, weeds; cleaner cut than round | Corners wear quickly ā shorter life than round |
| Twisted / Spiral | Aerodynamic spiral reduces noise; good cutting | Noise reduction, smooth cutting in grass | Moderate ā similar to round |
| Star / 5-point | Multiple cutting edges per rotation | Dense brush and thick grass | Wears quickly in hard materials ā best in grass |
| Serrated / Crossfire | Notched edges create micro-cutting surfaces | Cutting tough stems and weeds | Moderate ā notches can chip |
| Hexagonal (6-sided) | Flat sides provide cutting edges without sharp corners | Good all-around choice; longer life than square | Better than square; competitive with round |
Does Line Shape Actually Make a Difference?
Yes ā but the diameter matters more than the shape for most residential users. Here’s the practical breakdown:
- Round line: The safest choice. Lowest breakage rate, smoothest feeding through bump-feed heads, works with all head types. If in doubt, use round in the correct diameter.
- Square and hexagonal line: The sharp or flat edges cut more aggressively than round ā you’ll notice a slightly cleaner cut on heavy grass or weed stems. The downside is accelerated wear at the cutting edges.
- Twisted line: Primarily a noise-reduction feature ā the aerodynamic spiral reduces the whistling “whip” noise of standard round line by 10ā20%. The cutting performance is similar to round. Good choice if noise is a concern in residential settings.
- Star/multi-point line: High cutting efficiency in soft material (grass, light weeds), but the fine points break off in rocky, sandy, or woody material quickly. Best suited for well-maintained grass lawns.
What Line Material Should I Choose?
| Material | Properties | Best Use |
|---|---|---|
| Nylon (standard) | Most common, balanced durability and flexibility | General purpose ā all residential applications |
| Reinforced nylon (co-polymer) | Carbon fiber or titanium composite core | Heavy-duty cutting, longer life in tough material |
| Stihl Quiet Line / quiet nylon | Aerodynamic twist reduces noise | Noise-sensitive environments |
| Serrated nylon | Notched edges for aggressive cutting | Tough weeds and brush |
For most homeowners, standard nylon in the correct diameter is the best value. Reinforced or co-polymer lines cost more but last noticeably longer in commercial or heavy-duty conditions ā potentially 30ā50% longer between changes.
What Happens When You Use the Wrong Line
- Too thick: Motor bog, reduced RPM, overheating, excessive wear on the motor or gearbox. May not feed correctly through bump-feed heads.
- Too thin: Breaks constantly, poor cutting efficiency in heavy growth, frequent stops to extend line.
- Wrong shape for head type: Some fixed-line heads require specific pre-cut line ā round only. Multi-sided line in a head designed for round may not feed smoothly. Check head compatibility.
If your trimmer line keeps breaking, see our string trimmer line feed troubleshooting guide. If you need to replace the entire head, see our trimmer head replacement guide.
How to Choose the Right Line for Your Trimmer
- Check your trimmer’s manual for the recommended diameter range.
- Choose round line if you want maximum compatibility and longevity.
- Choose square or hexagonal if you cut dense weeds and want an aggressive edge.
- Choose twisted/quiet line if noise is a primary concern.
- Buy in bulk (large spool) rather than pre-cut packs ā significantly cheaper per foot of line.
- Match the brand recommendation when possible ā manufacturers test their trimmers with their own line and the specs are optimized. Generic line that’s slightly off-diameter can cause feeding problems.
Pro Tips
- Soak new round nylon line in water for 24 hours before spooling: Nylon absorbs moisture and becomes more flexible when wet, reducing breakage. This old-school trick still works and can extend line life noticeably in dry climates.
- Store unused line in a sealed bag or container: Nylon dries out and becomes brittle over time when stored loosely. Keep unused line sealed to preserve flexibility.
- Pre-cut fixed-line segments at the right length: Most fixed-line heads use 6ā9 inch segments. Pre-cut a batch before heading out and keep them in a pocket or pouch ā saves time in the field.
- For bump-feed heads, don’t over-wind the spool: Overfilling a bump-feed spool causes line to bind. Leave 1/8″ to 1/4″ clearance from the top of the spool cavity. See our guide on how to change string trimmer line for correct spooling technique.
Frequently Asked Questions
What is the most common string trimmer line size?
0.080″ is the most common size for residential cordless and light gas trimmers. 0.095″ is the most common for standard residential gas trimmers. These two sizes cover the vast majority of residential trimmer models.
What is the difference between round and twisted trimmer line?
Round line is a simple circular cross-section ā the most common, most compatible, and most durable shape. Twisted line has a spiral profile that reduces aerodynamic noise (the “whistle” during operation) by 10ā20%. Cutting performance is similar. Choose twisted if noise matters; choose round for maximum compatibility.
How long does string trimmer line last?
Depends heavily on use conditions. On smooth residential grass: a standard spool (0.080″ round, 50ā100 feet) lasts a full mowing season for most homeowners. In rocky or sandy areas, line breaks much faster ā sometimes 2ā3x more frequently. Reinforced co-polymer line significantly extends durability in abrasive conditions.
Can I use any brand of trimmer line in my trimmer?
Generally yes, as long as the diameter is within the manufacturer’s recommended range. Generic or third-party line works fine in most bump-feed heads. Some proprietary heads (like Milwaukee Auto-Feed or Stihl AutoCut) are optimized for their brand’s line and may work less smoothly with generic line.
Is pre-wound line better than buying a spool and winding yourself?
Pre-wound line cartridges are more convenient but significantly more expensive per foot of line. For homeowners who trim regularly, buying a large spool (100ā300 ft) and spooling the head manually is much more cost-effective. A 100-foot spool costs $8ā$15 vs. $5ā$8 per pre-wound cartridge that contains about 10ā20 feet of line.
Conclusion
For most homeowners, round nylon line in the correct diameter (0.080″ for cordless, 0.095″ for gas) is the right choice ā maximum compatibility, best longevity, and available everywhere. Upgrade to square, hexagonal, or co-polymer line when you regularly cut dense weeds or brush and want better cutting performance at the cost of faster wear. Always check your trimmer’s manual for the diameter range it supports.
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