Fixed-line heads don’t have a spool, a bump knob, or a spring — just a moulded head with one or two eyelets that a pre-cut length of line passes straight through. That simplicity is the appeal, but it’s also why people over-complicate the threading and end up with a head that throws line, vibrates, or won’t hold at all.
Which heads this covers
This guide is for fixed-line (sometimes called “eyelet” or “pre-cut”) heads, where you feed individual lengths of line straight through moulded holes in the head body, as opposed to bump-feed or auto-feed heads that wind a long length of line onto an internal spool. If your head has a bump knob on the base or a spool you wind line onto, this isn’t the right guide — those mechanisms, feed faults, and rewinding steps are covered separately. Fixed-line heads are common on lighter domestic strimmers and are popular with allotment and smallholding users precisely because there’s nothing inside to wear out.
What you need before you start
- Line of the correct diameter for your head — check the head body or your manual; most domestic fixed-line heads are rated 2.0-2.7 mm, with heavier units up to 3.5-4.0 mm.
- A tape measure or a pre-marked length of line as a template.
- Side cutters or heavy scissors for a clean, square cut (a ragged cut end is harder to feed through the eyelet and wears faster).
- The head off the shaft or at least accessible — some heads need a small retaining pin pushed through a locking hole to stop the head rotating while you work.
Safety first. Stop the engine, let the cutting head come to a complete stop, and disconnect the spark plug lead (or pull the battery on cordless models) before you touch the eyelets. A head that’s bumped or spun by accident while your fingers are near the holes is a genuine finger-injury risk, not a theoretical one.
Step-by-step: threading a fixed-line head
- Cut two equal lengths of line. Length depends on the head, but 20-25 cm per side is typical for compact domestic heads, giving a working cutting radius once trimmed to size after fitting. Cut both pieces from the same reel so the diameter and stiffness match exactly.
- Square off both cut ends. A clean, flat cut feeds through the eyelet far more easily than a torn or angled one, and reduces the chance of the line snagging on the eyelet’s inner edge on the way through.
- Feed the first length through one eyelet until roughly equal amounts protrude from each side, or until it seats against the internal stop moulded into most heads (this stop is what actually holds the line, not friction against the eyelet walls).
- Repeat for the second eyelet with the second length, keeping both lines seated the same way.
- Check both sides sit level. Hold the head up and sight along it — both line ends should stick out to roughly the same length. If one side is visibly longer, pull it back through and re-seat it.
- Refit the head to the shaft, following your machine’s normal fastening sequence, then trim both line ends to the same finished length using the head’s built-in line-length guide if it has one, or by eye against each other.
- Run it briefly at idle before cutting properly, and check for excessive wobble through the shaft — a small amount of head vibration is normal, a strong buzz usually means the two lengths still aren’t matched.
Getting the lengths right
| Head size (approx. cutting width) | Typical line diameter | Length to feed per side |
|---|---|---|
| Small domestic (23-30 cm) | 2.0-2.4 mm | 15-20 cm |
| Standard domestic (30-38 cm) | 2.4-2.7 mm | 20-25 cm |
| Heavier semi-pro (38-45 cm) | 3.0-3.5 mm | 25-30 cm |
Treat these as starting points, not fixed specs — always check the head body moulding or your manual, since manufacturers vary the eyelet size and internal stop position even at similar cutting widths.
Knots: mostly avoid them
Most fixed-line eyelets rely on the line seating against a small internal ridge or stop moulded inside the head, combined with the line’s own stiffness under centrifugal load — not on a knot. Tying a knot to “make sure it holds” is one of the most common mistakes with this style of head, and it usually backfires:
- A knot is thicker than the line either side of it, so it can jam partway through the eyelet instead of seating properly against the internal stop.
- The knot itself is a stress concentration point — line almost always snaps at the knot before it snaps anywhere else, so you lose length exactly where you don’t want to.
- Some cheaper aftermarket heads are moulded with a genuine knot-retention slot rather than an internal stop. If yours is one of these (check for a visibly wider slot at the eyelet mouth), a simple overhand knot is correct — but this is the exception, not the rule, so check before assuming you need one.
Common jams and quick fixes
- Line won’t pass through the eyelet at all — usually a ragged cut end catching on the eyelet’s inner lip, or line diameter slightly oversized for that particular head. Re-cut the end square and try again before assuming the eyelet is damaged.
- Line seats but pulls straight back out under load — the internal stop isn’t engaged, often because the length fed through was too short to reach it. Re-thread with a longer working length.
- Line flies out mid-cut — check for a cracked or worn eyelet edge (run a fingernail around the inside rim), which can let line slip past a stop that would otherwise hold it fine.
- One side keeps outlasting the other — near-always a length mismatch from the original threading, not uneven wear; re-cut both sides to match rather than trimming just the long one repeatedly.
When to call a dealer
Threading a fixed-line head is a five-minute job with nothing more than cutters and a tape measure, and there’s genuinely no reason to pay someone else to do it. The only time this tips into dealer territory is if the eyelet itself is cracked, elongated, or has broken away from the head body — moulded plastic eyelets don’t get repaired, they get replaced as part of a new head assembly. Given fixed-line heads are inexpensive, a cracked eyelet is a straightforward swap rather than something worth chasing a spare part for.