Black & Decker Trimmer Line Cap and Spring for AFS Trimmer

A small part that decides whether your trimmer works or sits in the shed

A string trimmer is only as reliable as the little cap that holds its spool in place. Mine finally cracked after a summer of trimming, and swapping in this replacement cap got me back up and running in minutes. I’ve since used it across a couple of Black+Decker AFS tools I keep around—primarily an LST420 (Type 2) and an older GH600—and I’ve formed a pretty clear picture of where this cap shines and where it comes up short.

Fit and compatibility

This replacement cap is designed for Black+Decker’s automatic feed spool (AFS) trimmers, and it’s broadly compatible across a long list of corded and cordless models. In my LST420, the cap clicked in cleanly, seated the spool securely, and restored normal line feed immediately. On the GH600, it was equally straightforward.

I did run into one nuance with a cordless unit: some of Black+Decker’s EASYFEED and other cordless models don’t require a spring. If your cap refuses to latch, or the feed feels overly tight after installation, try removing the spring and reinstalling the cap. That simple change made the difference on a friend’s unit that shares the same cap architecture. The included spring is helpful for AFS systems that expect it, but it’s not universal across all cordless types.

Tolerances on the latching tabs feel slightly different from the thicker OEM cap on a couple of models I tried. On one tool the fit was snugger than stock and needed a firm, even squeeze to click both tabs home. Once latched, though, it stayed put during trimming.

Installation: a five-minute fix

There’s nothing exotic here—installation is truly quick:

• Unplug the tool or remove the battery.
• Pop off the old cap by squeezing the side tabs.
• Verify whether your trimmer needs the spring; if it does, drop the spring into the hub first.
• Seat the spool (I use 0.065-inch line on AF-100 spools), making sure the line tails are routed through the eyelets.
• Align the new cap and press evenly until both tabs click.

Pro tip: If you’re fighting the cap, double-check that the spool isn’t overfilled or riding high on a tangle. An overstuffed or misseated spool will make any cap feel too tight and can lead to premature wear on the latches.

Day-to-day performance

With the cap installed, my trimmer’s automatic feed behaved as expected—line advanced smoothly on startup and during brief pauses, and I didn’t see the telltale symptoms of a cap that’s flexing or lifting (no sudden line starvation or repeated stops to tug line). On the LST420, I ran several weeks of mowing-season trimming around posts and fence lines without a hiccup.

I also used the trimmer as an edger along concrete, which is where the cap gets punished. The face of any cap will inevitably kiss the curb here and there, and this replacement cap shows wear in those scenarios faster than the original. After a season of weekly work (a small suburban yard), the plastic around the tabs showed whitening from stress and the rim had a good scuff pattern. Functionally it kept going, but this is a consumable, and the material feels a tick less robust than the OEM piece.

Build and materials

It’s a light, molded plastic cap with two integral latching tabs and a coil spring. The cap’s shape and dimensions match the AFS profile, and the spring has good tension out of the box. Compared to the original cap that shipped with my trimmer, the plastic here is slightly thinner on the tabs. That’s not a deal-breaker on its own—the design and geometry matter more than thickness—but it does mean you need to be mindful of two things:

• Don’t pry on the tabs with tools. Use finger pressure and press both sides evenly to release.
• Avoid running the cap hard along concrete for prolonged edging sessions. That’s where I saw the most accelerated wear.

If you treat it like a wear part and not an indestructible component, it holds up acceptably for regular homeowner use.

Line feed and spool pairing

This cap assumes you’re using the correct spool and line diameter for your trimmer—most Black+Decker AFS tools in this range use 0.065-inch line. Pair it with the right spool (I’ve had consistently good results with AF-100 spools), and the cap holds everything square and true. If you wind your own spools, take care not to overfill; an oversized winding will push outward on the cap, stress the tabs, and can cause intermittent feeding.

One subtle sign of a cap that isn’t seated perfectly: you’ll hear a faint rattle or see inconsistent feed after a bump or stop-restart. Reseat the spool, verify the spring orientation if your model uses it (wide end to the spool hub typically works best), and click the cap in until both tabs lock.

Durability and what to expect

After a full season of routine trimming and light edging, my first cap still latched, but the tab edges had stress marks and the face showed a lot of cosmetic wear. Late in the season, one latch finally gave up on a hard snag. The replacement cap I installed afterward is holding steady so far, and I’ve made a habit of keeping a spare in the drawer.

In short: it works, and it fits, but expect a shorter lifespan than the thicker original cap if you regularly edge against concrete or run the trimmer into rough borders. For lawn-only trimming, longevity is better.

Tips to get the most out of it

• Check spring requirement: Some cordless models don’t need the spring. If the cap won’t close easily, try without it.
• Seat the spool fully: A misseated spool is the number one cause of cap issues and poor feed.
• Use the correct line: 0.065-inch line keeps tension and feed within spec for these caps.
• Keep a spare: It’s inexpensive, and having a backup saves a weekend project if a tab snaps.
• Clean the head: A quick brush-out of debris before install helps the cap latch squarely and last longer.

Value

As a quick fix to keep an AFS trimmer alive, this replacement cap is easy to justify. It’s inexpensive, widely available, and restores function without fuss. Given the modest durability, the value equation really comes down to expectation: if you see it as a wear item that may need replacement after heavy edging or a long season, the math works. If you’re hoping for a lifetime part, this isn’t it.

Who it’s for

• Homeowners with compatible Black+Decker AFS trimmers who want a drop-in solution.
• Anyone who prefers prewound spools and consistent auto-feed.
• Users who mostly trim grass and light weeds, with occasional edging.

Who might want to keep two on hand: folks who edge along lots of hardscape or run their trimmer as a de facto edger every week.

The bottom line

I recommend this replacement cap for most Black+Decker AFS trimmer owners. It installs in minutes, restores proper auto-feed, and fits the intended models when installed correctly. The trade-off is durability: the plastic tabs and cap face wear faster than the original, especially with frequent edging against concrete. With that caveat—and a spare in the toolbox—it’s a practical, budget-friendly way to keep a solid trimmer working.