Verify the trimmer after maintenance

1. Match the model and parts

Remove the battery. Find LST300 and the adjacent type number on the tool label. Compare the guard, cap, spool and assembly figures with the linked LST300 manual. Use ServiceNet for your exact type if they differ. LST300 is not a bump-feed head.

Region: US

Parts: Automatic-feed head with AF-100 spool; match model and tool type to manual

Not covered: LST420 / LSTE525; GH corded models; Dual-line heads; Metal line or blades; Nonmatching tool type or modified head; Unknown tool type or missing exact-type manual; Bump-feed conversion.

Choose the versions you can confirm.

2. Prepare

3. Follow your checks

4. Follow and record

Complete the checks before recording physical work. Follow steps in order.

1. Record the exact tool and make it safe

   Release the trigger, let the head stop, engage the lock-off and remove the battery. Leave it removed throughout hands-on care. Keep fingers away from the sharp cutter on the guard. Read LST300 and the tool type from the label. Open the official model/type lookup and compare its manual and parts figures with your actual guard, single-line head and AF-100 spool. A readable model name alone does not establish the type. If the exact type manual cannot be obtained, or any figure differs, save a preparation record and stop.

   Look for: The battery is physically separate from the tool; your label type and matching manual reference are written below.

   Tool type exactly as printed on the label *Exact-type manual reference or link that you matched *I completed this step and checked the observation.
   Manual: Official model/type lookup instructions; type is beside or below the model number

2. Check the completed assembly with power removed

   Check the guard screw, both cap tabs, auxiliary handle and tightened height collar. Confirm round 0.065 inch (1.65 mm) nylon exits the eyelet and reaches no farther than the guard cutter.

   Look for: Every user-adjusted part is secure and no line is trapped under the cap.

   I completed this step and checked the observation.
   Manual: English pp9–10 Replacing the spool; figs M–O

3. Prepare the normal working area

   Clear wire, cord and loose objects from a dry outdoor area. Wear the manual’s required eye and hearing protection, long pants and substantial footwear. Keep people and pets away; edging requires at least 100 feet (30 m) clearance.

   Look for: The ground and area are suitable for normal trimming, with clear separation from bystanders.

   I completed this step and checked the observation.
   Manual: English pp2–3 Safety; p8 Installing and removing the battery pack

4. Choose whether to run a normal-use check

   You may leave the battery out and record untested. To check operation, only after assembly and area checks pass, insert the undamaged matching battery fully until latched. Keep eye protection on whenever the pack is installed.

   Look for: Your record will distinguish an unpowered check from an observed running result.

   I completed this step and checked the observation.
   Manual: English pp2–3 Safety; p8 Installing and removing the battery pack

5. Observe normal control and feed

   If testing, follow the manual stance and normal lock-off/trigger controls. Keep the guard at least 24 inches (609.6 mm) from your feet, cut with the line tip and never bump the head. Stop if feed fails, running is slow or vibration is abnormal.

   Look for: Record only what you observe during ordinary use; no hands approach the rotating head.

   Normal-use observation *Choose an observationNormal control and feed observedSymptom remains; leave unusedPowered check not performedI completed this step and checked the observation.
   Manual: English pp8–9 Height adjustment / Operating the trimmer; figs I, J1

6. Stop before any further inspection

   Release the trigger and wait for the head to stop. Remove the battery before touching the cap, guard or line again. A trigger that cannot switch the tool off requires service; keep clear of moving parts and do not handle the head.

   Look for: The head has stopped and the battery is removed before hands-on inspection resumes.

   Remaining symptom or next action *I completed this step and checked the observation.
   Manual: English pp2–3 Safety; p8 Installing and removing the battery pack

7. Record an observed or untested result

   Choose normal operation observed, symptom remains, or powered check not performed. Record any remaining symptom for support. If feed or slow running persists after the corresponding user checks, leave the tool unused and contact service.

   Look for: The result accurately describes whether the normal-use check happened and what it showed.

   Result of this task *Choose an observationChecks passed; ready for the stated next stepMore preparation or a linked task is neededLeave unused and contact serviceI completed this step and checked the observation.
   Manual: English pp10–11 Automatic line feed does not work; figs N, Q, R

5. Keep your result

Record what you observed. A completed checklist does not certify that equipment is repaired.

When to check again

After user maintenance, spool replacement or adjustment

Verify assembly after each care task and before returning to normal use.

Sources & fit

• BLACK+DECKER LST300 instruction manual (manufacturer document, retailer-hosted)English pp8–10 Assembly, Operating instructions, Replacing the spool; pp2–3 Safety · Checked 2026-10-13
• BLACK+DECKER: locate a manual using model and type numberOfficial model/type lookup instructions; type is beside or below the model number · Checked 2026-10-13
• BLACK+DECKER LST300 product and supportLST300 model identity; Automatic Feed Spool; Includes AF-100 · Checked 2026-10-13

Independent, AI-assisted guidance. No physical repair trial is claimed. Manufacturer instructions for your exact version take priority.

Related tasks

• Replace the cutting-line spool
• Check automatic line feed failure
• Check a trimmer running slowly