• 18 parts
  • Checked September 2026

Parts of a String Trimmer

A string trimmer from the side, then its engine and its head close up.

Parts of a String Trimmer

Name Date

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
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Write the name of each numbered part.Answer key

  1. Engine
  2. Rear handle
  3. Throttle trigger
  4. Loop handle
  5. Shaft
  6. Fuel tank
  7. Fuel cap
  8. Starter handle
  9. Air filter
  10. Choke lever
  11. Primer bulb
  12. Spark plug
  13. Muffler
  14. Trimmer head
  15. Spool
  16. Line
  17. Debris shield
  18. Cut-off knife

Drawn for this site on 2026-09-30 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

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All 18 parts on the diagram

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Whole tool 5

  1. Engine A small gasoline engine at the top end of the shaft. It spins the head at the other end.
  2. Rear handle The grip next to the engine, for one hand. The throttle trigger sits under it.
  3. Throttle trigger It controls engine speed. Squeezing it makes the engine, and so the line, turn faster.
  4. Loop handle The front handle, for the other hand. A loop clamped to the shaft.
  5. Shaft The long tube from the engine down to the head. A drive shaft turns inside it.

Engine 8

  1. Fuel tank It holds the fuel for the engine.
  2. Fuel cap It covers and seals the opening of the fuel tank.
  3. Starter handle The handle on the starter rope. Pulling it turns the engine over to start it.
  4. Air filter Cleans the air on its way into the engine. The filter is under this cover.
  5. Choke lever It opens and closes the choke, which helps a cold engine start.
  6. Primer bulb A soft bulb pressed before starting. It draws fuel into the carburetor and pushes the air out.
  7. Spark plug It makes the spark that lights the fuel mixture in the cylinder.
  8. Muffler It quiets the exhaust of the engine.

Head 5

  1. Trimmer head The spinning head at the bottom of the shaft. The spool of line sits inside it.
  2. Spool The reel inside the head. The spare line is wound on it.
  3. Line Nylon line that whirls fast enough to cut grass and weeds. It wears away as it works.
  4. Debris shield The guard on the operator's side of the head. It stops some of what the line throws back.
  5. Cut-off knife A small blade on the debris shield. It trims the line to the right length as new line feeds out.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. (1) A maker's operator's manual for a gasoline grass trimmer, https://archive.org/details/manualsonline-id-d15bb57d-4804-4c34-3dc5-2cea379739c3 (its numbered description: power head and engine, drive shaft, loop handle, rear handle, throttle trigger, debris shield, nylon cutter head, cut-off knife, air cleaner, choke, starter handle, fuel tank, fuel tank cap, spark plug, muffler). (2) A second maker's owner's manual for a gasoline trimmer, https://archive.org/details/manualsbase-id-644170 (engine, loop handle, throttle trigger, debris shield, cutting-line head, spool, cutoff knife, choke lever, primer bulb, starter grip, fuel tank, fuel cap, air filter, spark plug, muffler). (3) A third maker's manual for a light gasoline trimmer, https://archive.org/details/manualsbase-id-450484 (engine, throttle trigger, assist handle, debris shield, trimmer head, spool, trimmer line, line limiter blade, primer bulb, choke lever, starter handle, fuel tank, fuel cap, air filter, spark plug, muffler). (4) A maker's manual for an electric string trimmer, https://archive.org/details/manualzilla-id-5786268 (rear handle, front handle, shaft, spool, line, cut-off blade). (5) Wikipedia, String trimmer, text only, https://en.wikipedia.org/wiki/String_trimmer (the line, the long shaft topped by a gasoline engine, the trigger-activated throttle on the handle, the trimmer head and its spool, the shield on the user's side). No maker is named. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; own work, no maker's model copied. Licence: own work

How it works

These are the parts of a gasoline string trimmer with a straight shaft, the tool often called a weed eater. The first view is the whole tool, the second is the engine, and the third is the head, cut open.

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From the engine to the head

The engine sits at the top end of the shaft. One hand holds the rear handle, with the throttle trigger under it, and the other holds the loop handle. At the bottom, the trimmer head spins the line; spare line is wound on the spool inside. The debris shield covers the operator's side, and its cut-off knife trims the line to length.

On the engine

The fuel tank and its cap hang under the engine. The air filter, choke lever and primer bulb are at the front, the spark plug is on top of the cylinder, the muffler is behind it, and the starter handle is at the back.

  • An electric string trimmer has a motor in place of the engine, but the same head, spool, line and shield.

Questions and answers

What are the parts of a string trimmer called?

An engine or motor, a shaft, a rear handle with a throttle trigger, a front or loop handle, and a trimmer head. The head holds a spool of nylon line, and a debris shield with a cut-off knife sits over it.

What is the spool on a string trimmer?

The spool is the reel inside the trimmer head. Spare line is wound on it, and the two ends of the line come out through the sides of the head.

What does the debris shield do?

It is the guard over the operator's side of the head, and it stops some of what the line throws back. A small blade on it, the cut-off knife, trims the line to the right length.

What is the primer bulb for?

It is a soft bulb on a gasoline trimmer's engine. Pressing it clears air from the carburetor and fuel lines and puts fuel in them, so the engine starts with fewer pulls on the starter rope.

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