What breaks first on this head
The KLS 124-03 is the head on roughly every blue-and-black Kobalt 24V trimmer sold at Lowe's over the last five years. Two things fail on it, reliably. The factory spool's pre-wound line binds into the feed notches after its second refill, which is why the tool stops auto-feeding after about an hour of total runtime. And the bump knob, which is pure ABS, cracks along the internal thread when somebody taps it hard on concrete instead of turf.
Neither of those requires a trip to the dealer. The whole repair takes ten minutes and costs less than a coffee if you buy the universal 0.080 pre-wound loop that fits the M10 x 1.25 LH spindle.
01 — Remove the battery and lay the trimmer down
Before anything else, pull the 24V pack off the back of the tool. Kobalt's trigger is a momentary switch, but the controller can still pass brief current to the head if the tool is bumped while a battery is attached.
Flip the trimmer so the head is pointing up at you, and rest the shaft on a towel or kraft paper. A little cushioning keeps the throttle housing from scuffing.
02 — Unthread the bump knob
The bump knob is the round black plastic cap on the underside of the head. It's reverse-threaded, because the head spins clockwise in use. To loosen, rotate clockwise. Many first-timers over-tighten it trying to loosen counter-clockwise; a cracked bump knob is almost always the result.
With the trimmer upside-down, a firm quarter turn is enough to break it free. Unthread fully by hand from there.
03 — Lift out the old spool
With the knob out, the inner spool lifts straight up. The compression spring under it will try to pop out; catch it. If the line is still attached to the feed notches and fighting you, cut it with shears. There is no reason to salvage it.
Inspect the feed-notch openings in the head casting. If they have widened into ovals, the head itself is worn and a new spool will start binding again within the season. That is the moment to swap the whole head, not just the spool.
04 — Drop in a pre-wound 0.080 spool and reassemble
Our replacement spools are pre-wound with a true 0.080 inch line and ship with the ends pre-fed through the feed eyelets. Drop the spool into the cavity, orienting it so the line ends pass out through the two notches.
Set the spring back on top of the spool. Thread the bump knob back on counter-clockwise, hand-tight only. Over-torque it and you will crack the thread later.
Reinstall the battery. A quick test pull on the trigger should spin the line cleanly; if the line tangles inside the head, the spool is seated upside-down. Unthread, flip, and reseat it before trimming along hard edges.
When to replace, not just respool
A spool swap is good for about a season of typical suburban use. Two signs that the next fix is a full head replacement rather than another spool: the feed notches are oval, and the bump knob thread inside the head has chewed itself rough.