Stihl SuperCut 20-2 vs AutoCut 40-2 (Field Test)
The SuperCut 20-2 feeds line automatically while it runs; the AutoCut 40-2 feeds when you tap its rotating head on the ground. Neither is the better choice for every job. First confirm your trimmer manual lists the exact head, then compare feed reliability, line use, and cutting pace with the same machine and conditions.
If your trimmer is ready for the season but its head keeps interrupting the job, the feed system matters. The SuperCut 20-2 and AutoCut 40-2 are both two-line nylon mowing heads, but they handle line differently. That changes how you work and what you need to watch during a test.
My practical pick depends on the task: consider the SuperCut when automatic feed suits your trimming routine; consider the AutoCut if you prefer to control feed by tapping the head. Those are starting points, not proof that either head fits your machine. STIHL fitment is specific to the trimmer and head revision. Check the machine manual and head markings before buying or installing.
A fair comparison also needs to separate design from results. I can describe how each feed system works, but I won’t claim one cut faster or used less line without measured test data. The method below lets you make that comparison on your own machine without guessing at fitment or operating limits.
Equipment Setup and Safety Preparation
A valid comparison starts with safe, correct fitment. The head must be listed for your exact trimmer, and the manual must specify the right interface and retaining parts. A matching name or thread alone does not confirm compatibility, safe rotation, or the right guard.
- Check fitment first. Find your machine’s model information and consult its STIHL instruction manual. Confirm that the specific SuperCut 20-2 or AutoCut 40-2 revision is listed. Follow the manual for the gearbox interface, rotation direction, retaining hardware, and tightening method. Do not force a head onto the gearbox or rely on apparent thread compatibility.
- Check limits and materials. Use only the line type and diameter approved for that head and machine. Maximum operating speed and permitted line can vary by model and head revision. Read the manual and head markings rather than applying a specification from another trimmer.
- Prepare the work area. Wear eye or face protection, hearing protection, gloves, long trousers, and sturdy footwear. Clear loose objects and keep people at least 15 m (50 ft) away. Inspect the guard, gearbox, head, and line before starting.
- Install and start by the book. Use the specified hardware and tightening procedure. Check that the head turns freely and that the correct guard is in place. Start and warm the machine as its manual directs. Never start with the head touching the ground or near other people.
A cracked, loose, or incorrectly retained head can break apart at operating speed. Stop if you notice vibration, looseness, cracks, or abnormal noise. Do not keep trimming with a damaged head or a missing or incorrect guard.
Illustrative fitment check: Imagine one trimmer owner sees that a replacement head appears to match the gearbox thread. That is not enough to install it. The owner checks the machine manual for the head listing and hardware, then confirms the guard and operating limits. If the manual does not list that head, the safe next step is to find an approved option, not to test the fit by running it.
Field Test: Trimming Performance and Line Feed
The SuperCut advances line automatically during operation; the AutoCut advances line when you tap its rotating head against the ground. A useful field test keeps other factors steady so you can compare the two feed methods, cutting pace, line use, and interruptions on your own equipment.
Before comparing, confirm again that both heads are approved for the same trimmer. Use the same approved line type and diameter only if both head manuals allow it. Load each head according to its own instructions; do not assume their loading methods are alike.
Choose one patch of similar vegetation and use the same operator, machine, throttle approach, and cutting path for each trial. Keep the line length and starting conditions consistent where the manuals allow. Avoid mixing grass, dense weeds, and woody growth into one result: the changing conditions make the comparison harder to read.
| What to compare | SuperCut 20-2 | AutoCut 40-2 | What to record |
|---|---|---|---|
| Feed action | Line advances automatically during operation | Tap the rotating head against the ground to advance line | Whether feed is reliable and when it occurs |
| Operator input | Let the head feed as designed | Tap only as instructed, on a suitable surface | Number of feed interruptions or taps |
| Cutting pace | Time the same marked area | Time the same marked area | Elapsed time and area completed |
| Line use | Check line before and after | Check line before and after | Amount used, using the same measuring method |
| Downtime | Note feed or line-loading stops | Note feed or line-loading stops | Time spent stopping or correcting feed |
Run each comparison more than once if conditions stay similar. A single pass can be skewed by a thicker patch, a different cutting angle, or an uneven surface. Record what happened rather than treating a short trial as a universal ranking.
With the SuperCut, follow its automatic feed design; do not use AutoCut-style tapping unless that head’s instructions call for it. With the AutoCut, tap only as instructed. A hard or unsuitable surface can damage the head, and tapping technique can affect how often you stop to feed line.
Illustrative field comparison: If an owner trims a narrow lawn edge and then a patch of taller grass, those are two separate tests. The first can show whether feed interruptions affect edging pace; the second can show how each head behaves in heavier growth. Without timing and line-use records, saying one was “faster” would be a guess.
Maintenance, Inspection, and Line Loading
Regular checks help explain poor feed before you blame the head. Stop the engine or remove the battery before handling it, and let hot parts cool. Clear wrapped vegetation, look for damage, and reload only with line and a method approved for that exact head revision.
After each test, inspect the head for cracks, wear, loose parts, or signs of impact. Check that the line is not tangled or trapped and that the retaining hardware remains secure according to the manual. If you find damage, stop using the head and follow STIHL’s repair or replacement guidance.
Line diameter and loading method are not safe to infer from a head’s name alone. Check the markings and instructions for the exact revision. If line feeds poorly, first review whether it is the approved type, whether it was loaded correctly, and whether vegetation is wrapped around the head. Do not substitute wire, metal line, or another unapproved cutting material.
| Symptom | Check first | Safe next step |
|---|---|---|
| SuperCut does not feed as expected | Approved line, correct loading, and wrapped vegetation | Stop the machine and consult the head instructions |
| AutoCut does not feed after a tap | Correct loading and the specified tapping method | Use only the instructed method and suitable surface |
| Vibration, crack, or abnormal noise | Head condition and retaining parts | Stop at once; do not operate until the cause is addressed |
| Line breaks often | Approved line and head markings | Replace with specified line; do not increase diameter by guesswork |
A head that looks intact can still be wrong for a particular machine. If the manual does not confirm the fit or you cannot identify the correct parts, pause and check with a STIHL dealer rather than experimenting.
Storage and Seasonal Care
Seasonal storage should leave the head clean, sound, and ready for its next inspection. Remove grass and debris after use, check the line and head, and store the machine as its manual directs. Before the next start, repeat the fitment and safety checks instead of assuming last season’s setup is still correct.
Keep the instruction manual with your equipment records, along with the head revision, approved line details, and any issues you noted during testing. This makes it easier to reload correctly and compare results later. Store the tool and accessories in a dry place as directed by the machine manual.
If the trimmer uses a STIHL two-stroke or 4-MIX engine, follow that engine’s fuel specification. STIHL two-stroke oil is commonly used at 50:1 in applicable STIHL two-stroke machines, but do not apply that ratio without checking the manual. Battery tools and four-stroke engines have different instructions; the fuel ratio does not apply to a battery machine.
Before the first seasonal job, inspect the head, guard, gearbox, and line, then confirm the machine still lists that head and its hardware. If anything is cracked, loose, or unclear, resolve it before starting.
Which Head Should You Choose?
The best choice is the head that is approved for your machine and whose feed method fits your work. Automatic feed reduces the need for the operator to tap for line; bump feed gives the operator a direct feed action. Your own controlled trial can show which causes fewer interruptions and suits your trimming routine.
Choose the SuperCut 20-2 if its automatic feed is listed for your trimmer and you prefer line to advance during operation. Choose the AutoCut 40-2 if it is listed and you prefer bump feed, with line advanced by tapping as instructed. Compare measured results on the same task; don’t rely on the head name or an unverified speed claim.
Frequently Asked Questions
These quick answers cover the main fitment, feed, and safety points. Always use the instruction manual and markings for the exact machine and head revision; the names alone do not set fit, line size, or operating limits.
What is the main difference between the SuperCut 20-2 and AutoCut 40-2?
The SuperCut feeds line automatically during operation; the AutoCut feeds when its rotating head is tapped on the ground.
Are both heads two-line mowing heads?
Yes. Both are two-line nylon mowing heads, not chainsaw attachments.
Will either head fit any STIHL trimmer?
No. Use a head only when the specific trimmer manual lists it and its required interface and hardware.
Can I choose a line diameter based on the head name?
No. Confirm the approved line diameter and type on the head markings and in the instructions for that revision.
Should I tap the SuperCut head to feed line?
Follow the SuperCut instructions. It feeds automatically during operation; do not assume it uses the AutoCut method.
How should I feed line on the AutoCut 40-2?
Tap the rotating head only as instructed and on a suitable surface.
What should I do if the head vibrates or makes an unusual noise?
Stop immediately. Inspect for damage or looseness, and do not operate until the cause is addressed.
Can I use wire or metal line in either head?
No. Use only the approved cutting material specified for the head and machine.
Does the 50:1 fuel ratio apply to battery trimmers?
No. Battery trimmers use no fuel mix. Check the manual for the exact engine type and its fuel specification.
Which head cuts faster?
There is no universal result established here. Test both only if approved for your machine, using the same line, vegetation, area, and technique.
(This article was written by one of our staff writers, Harrison Croft. Visit our Meet the Team page.)
