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How to check a used monitor arm
A monitor arm is a gas spring, a few castings and some hardware, and exactly one of those parts wears out. A spring that has lost its tension will hold your screen for about a week and then start creeping downward, and there is no adjustment that brings it back.
The short answer
Load it with a screen of the weight you intend to use and leave it for ten minutes. If it drifts at all, the spring is finished — and on most arms the spring is not a serviceable part.
Get these first
One test that matters, and the hardware nobody keeps
- Mount a screen of your intended weight and leave it in position for ten minutes. This is the test. A tired gas spring holds briefly and then creeps down under sustained load, and a two-second demonstration in a shop will not reveal it. Set the height, walk away, come back and look.
- Check the supported weight range at both ends. Arms have a minimum as well as a maximum, and a light monitor on an arm rated for heavy ones will float upward and refuse to stay low just as surely as a heavy one sags. Weigh your screen — the figure on the specification sheet often excludes the stand you removed.
- Confirm the VESA pattern and the screw length. 75x75 and 100x100 are standard, but larger screens use 200x100 or 200x200 and need an adapter plate. Screw length matters too: too long and you can damage the panel, too short and it will not hold. The correct screws are model-specific and are the first thing to go missing.
- Check both mounting options are present — the desk clamp and the grommet hardware. Arms ship with both; sellers keep whichever they used and lose the other. If your desk needs the grommet mount and only the clamp survives, you are buying a part you will have to source separately.
- Work every joint through its full range and listen. Each joint should move with firm, even resistance and stay where you leave it. A joint that is loose at one point in its travel or that clicks is worn, and on arms with plastic bushings that wear is not recoverable.
- Test the tilt and rotation locks under load. Many arms hold height well but let the screen tilt forward slowly under its own weight. Set a tilt angle with the screen mounted and check it again after the ten-minute wait, at the same time you check the height.
- Inspect the clamp jaws and the desk contact faces. Over-tightened clamps deform, and a deformed jaw grips a desk edge unevenly. Check the rubber or felt pads are still present — without them the clamp will mark your desk and grip less well.
- Look for cracks around the mounting plate and at the base of the main post. These are the high-stress points. A hairline crack there is holding a screen above your desk, which makes it the one cosmetic flaw in this category worth walking away over.
The one nobody checks
Sustained load. A gas spring that has lost tension still feels fine for the first few seconds, which is exactly how long a demonstration lasts. Mount a screen at the weight you actually intend to use, set the height, and go and do something else for ten minutes. That single wait is the difference between an arm that works for years and one that sinks a little further every day.
Note
Weight range is a range, and people only read the maximum. Putting a light 24-inch panel on an arm designed for a heavy 34-inch ultrawide gives you a screen that drifts upward and will not stay low, which is just as irritating as one that sags. Weigh your monitor with the stand removed and match it to the middle of the range, not the end of it.
What to measure
Higher is better▲Higher is betterLower is better▼Lower is betterMust be zero∅Must be zeroMust match the spec=Must match the spec
What a used arm has to prove
| Metric | Which way | What it tells you | Healthy looks like |
|---|---|---|---|
| Height drift under load | Must be zero | Whether the gas spring still has tension. | No movement after ten minutes with your screen mounted. Any creep is terminal. |
| Your screen weight vs the range | Must match the spec | Both ends of the rating, not only the top. | Comfortably inside. Too light floats up, too heavy sags. |
| VESA pattern and screws | Must match the spec | Whether it physically attaches to your monitor. | Correct pattern, correct screw length, adapter plate if needed. |
| Clamp and grommet hardware | Higher is better | The half of the mounting kit that always goes missing. | Both present. You need whichever your desk requires. |
| Joint resistance | Must match the spec | Wear in bushings that are usually not serviceable. | Firm and even through the full range. No clicking, no loose spots. |
| Tilt hold under load | Must be zero | A separate failure from height drift. | Angle unchanged after the same ten-minute wait. |
| Clamp jaw condition | Must be zero | Deformation from over-tightening. | Flat faces, pads present, even grip on a desk edge. |
| Cracks at stress points | Must be zero | A structural failure suspended above your desk. | None at the mounting plate or the base of the post. |
Walk away if
Walk away if
- Any downward creep after ten minutes under load.
- A tilt angle that changes on its own.
- Missing grommet hardware when your desk needs it.
- The wrong VESA pattern with no adapter included.
- A joint that clicks or has a loose spot in its travel.
- Deformed clamp jaws or missing pads.
- A hairline crack anywhere on the mounting plate or post.
What each fault is worth
Bring the measurement, not the opinion. Name the fault, name the fix, name what the fix costs — that is a solvable problem with two acceptable answers, which is what makes it work.
| What you found | What it actually costs | What to ask for |
|---|---|---|
| Height creep | A spring that is not serviceable on most arms. | Walk away. This is the whole product. |
| Missing grommet or clamp kit | A part you must source separately. | Its real cost, if it is even sold. |
| Wrong VESA pattern | An adapter plate. | Adapter cost, and confirm one exists for your screen. |
| Worn joints | A screen that will not stay put. | A large discount, or skip it. |
| Crack at a stress point | A structural risk over your desk. | Walk away, at any price. |
Ready to go looking?
Take the checklist with you, then browse what is listed. Everything on this page works just as well the other way round when you are the one selling.
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