Last Updated on July 14, 2026 by D. Ruddy
Your Black and Decker trimmer loses cutting power when the line breaks. This guide shows how to replace black and decker weed wacker string with simple steps.
Quick Verdict: Simply put, replacing the string on a Black and Decker weed wacker takes under 10 minutes. You open the spool cap, remove old line, wind new 0.065-inch monofilament, and snap it back. AutoFeed models bump to release more line automatically.
Key Takeaways
- Replacing the string on a Black and Decker weed wacker takes about 5 to 10 minutes with the spool system.
- The AF-100 spool holds up to 30 feet of 0.065-inch line according to Black and Decker specifications.
- You do not need special tools to swap the string on most Black and Decker electric trimmers.
- AutoFeed bump heads release new line when you tap the trimmer on the ground during use.
- Using the wrong line diameter can jam the spool and reduce cutting performance on your weed wacker.
What Is a Black and Decker Weed Wacker Spool?
A spool is the plastic hub that holds the cutting line inside the trimmer head. The Black and Decker brand uses a removable spool for quick reloads.
Most current models use the AF-100 spool design. This spool fits many string trimmer units from the manufacturer. The hub is made from tough ABS plastic to survive impacts.
The spool works with popular models such as the GH900, GH400, and LST300. You can buy these at Home Depot or direct from the brand.
The internal chamber keeps the line coiled and protected from dirt. A small spring sits below the spool to push it upward during bump feeds.
- The spool stores monofilament line in a coiled chamber beneath the cap.
- A spring and eyelets guide the line out through the trimmer head sides.
- The AutoFeed system advances line when the user bumps the head on grass.
- Some spools come pre-wound to save time during replacement tasks.
- The hub has arrow marks that show the correct winding direction for line.
Tip: Buy two AF-100 spools so you can swap a loaded one while you rewind the empty.
How Does the AutoFeed System Work?
The AutoFeed mechanism uses a bump knob at the base of the trimmer. When you tap it, a clutch releases more line.
According to the Outdoor Power Equipment Institute, over 80 million US households use outdoor power equipment like string trimmers currently.
The spool sits on a spring loaded shaft. Rotation creates centrifugal force that pushes line outward. A blade on the guard cuts stray line to length.
This design removes the need for manual line pulls. The user simply taps the head to keep the cutter fed during work.
- The spring pushes the spool upward when you press the bump knob down.
- Rotation twists the spool and feeds line through the eyelets slowly.
- A blade on the guard trims excess line to the correct cutting length.
- The system stops feeding when line reaches the safe maximum extension.
The string trimmer design keeps line at safe lengths for efficient cutting. This reduces motor strain and extends tool life.
What Are the Signs You Need New String?
Watch for clear clues that your line is spent. Early action keeps your yard neat and prevents motor overload.
- The line ends shrink below 2 inches on both sides of the head.
- The trimmer leaves tall grass uncut in a single pass.
- You hear the motor spin faster but see no cutting action.
- The AutoFeed bump produces no new line during normal use.
Warning: Do not run the trimmer with no line. The head can overheat and damage the spool housing.
What You Need Before You Start
Gather a few items before you open the trimmer head. Preparation makes the how to replace black and decker weed wacker string task smooth.
- New 0.065-inch monofilament line or a pre-wound AF-100 spool.
- A clean cloth to wipe dirt from the spool housing area.
- Work gloves to protect your hands from the cutting edges.
- Safety glasses to block debris when the head is open.
- A small scissors to trim line ends after winding if needed.
Important: Confirm your model uses the AF-100 spool by checking the label near the handle.
Step-by-Step Process
Follow these steps to reload your trimmer with fresh line. This method works for most electric Black and Decker models.
- Disconnect power by unplugging the cord or sliding out the battery pack.
- Flip the trimmer so the head faces up and locate the spool cap on bottom.
- Press the tabs and pull the cap off to expose the spool and line cavity.
- Remove the old line and any broken pieces from the spool and eyelets.
- Cut a 15 to 30 foot length of 0.065-inch line for manual winding jobs.
- Insert one line end into the anchor hole on the spool inner hub.
- Wind the line tightly around the spool in the direction of the arrows.
- Leave about 6 inches out and thread it through the eyelet on the cap.
- Snap the spool into the housing and press the cap until it clicks.
- Pull the line end to seat it, then reconnect power and test the feed.
Step three requires firm thumb pressure on the two side tabs. The cap pops upward when both tabs release at the same time.
Step seven is critical. Wind the line in the arrow direction only. Backward winding causes tangles that block the eyelets.
After step nine, give the line a gentle tug. It should resist but move slightly. This confirms proper seating in the anchor.
What to Expect
The job is fast and low cost. Most users finish in under 10 minutes after the first try.
According to Consumer Reports, you should check trimmer line every 3 mowing sessions for best results.
| Task | Time | Cost |
|---|---|---|
| Buy pre-wound spool | 2 minutes | $5 to $10 |
| Manual line winding | 5 to 10 minutes | $3 per 30 ft roll |
| Full head cleaning | 15 minutes | $0 |
The how to replace black and decker weed wacker string process saves money versus hiring a yard service. A single roll of line costs less than one visit from a landscaper.
| Model Series | Spool Type | Line Diameter |
|---|---|---|
| GH400, GH500 | AF-100 | 0.065 inch |
| LST300, LST400 | AF-100 | 0.065 inch |
| ST7700 stand model | SF-080 | 0.080 inch |
The tables above show common fitments. Always check your manual before buying a spool to avoid mismatch.
Common Mistakes to Avoid
- Using line thicker than 0.065 inch because it j
