Gas spring vs mechanical counterbalance

“Monitor arm” describes three different machines. They look alike in a photograph, they cost roughly the same, and they solve the problem in ways that are not variations on a theme — they are genuinely different mechanisms with different failure modes.

The distinction is worth twenty minutes of your life because it decides one thing no listing puts on the front: whether your monitor has to be heavy enough for the arm to work.

Counterbalance, and why it needs a range

Start with the idea that both spring designs share, because everything else follows from it.

A counterbalanced arm does not hold your monitor up in the way a shelf holds a book up. It pushes back. Inside is a spring, tensioned to push upward about as hard as your monitor pulls downward. When the two roughly cancel, the monitor weighs almost nothing as far as the arm is concerned — nudge it with a finger and it moves; let go and it stays. That floating feel is the entire reason to buy one of these.

But a spring can only be tensioned within a range, and this is where the whole thing turns:

Too heavy and your monitor beats the spring. The arm sags, and tightening the adjustment screw eventually runs out of screw. That is the failure everyone anticipates, and it is why the maximum gets printed on the box.

Too lightand the spring beats your monitor. The arm creeps upward, or refuses to stay where you put it, or springs to the top of its travel the moment you let go. You wind the tension down to its minimum and it still climbs. This failure is just as real, just as common, and almost never advertised — which is why people conclude they have received a faulty arm when what they have received is an arm for a heavier monitor.

So every counterbalanced arm has a floor and a ceiling. Ergotron’s LX is 7–25 lb. The LX Pro is 4–22 lb. The HX is 20–42 lb— an arm that will not hold a normal monitor up at all. Humanscale’s M2.1 is 5–15.5 lb. Every one of them publishes a minimum, and every listing leads with the maximum.

Gas spring

The most common mechanism, and the one in most arms under $200.

A gas spring is a sealed pneumatic cylinder: a piston in a tube of compressed gas, usually nitrogen. Compressing it pushes back, the same way a car’s tailgate strut or an office chair’s height cylinder does. You tune the push with an adjustment screw that changes the leverage the cylinder acts through.

Ergotron calls their implementation “Constant Force”— their term, and worth using precisely because it is theirs rather than an industry classification. The name points at the goal: force that stays even across the travel, so the monitor behaves the same near the desk as it does at the top of its lift.

What you get is cheap, compact, smooth, and easy to adjust with one hex key. What you are trusting is a gas seal. A cylinder that loses pressure loses lift, and that is the classic long-run complaint about gas-spring arms — the monitor that used to float now drifts down by evening.

We want to be careful here, because this is exactly where a review site would cheerfully tell you gas springs die and mechanical springs do not. We have no failure data.We have not tested these arms, we have not cycled one to exhaustion, and we are not going to imply a lifespan from a mechanism’s reputation. What we can point at is what the makers are willing to promise, which is a real and checkable thing — and there, ten years from Ergotron against one year from the cheapest gas-spring arm we looked at tells you the manufacturers do not consider these interchangeable either.

Mechanical spring counterbalance

Same idea, no gas. Instead of a sealed cylinder, a coiled steel spring works through a linkage.

Humanscale calls theirs “Weight-Compensating Spring Technology”— again, their term. The M2.1 is the example on this site, and the way Humanscale documents it is the most interesting thing about it.

Their installation manual describes an adjustment screw that raises or lowers lift force, with a diagnostic that is refreshingly plain: “If the arm rises up on it’s own, the lift force is too high… If the arm falls down with the weight of the monitor, the lift force is too low”. That is both failure modes, described in one paragraph, in the box — the too-light case stated as openly as the too-heavy one.

The M2.1 also carries a counterbalance indicatoron the upper arm: a small window showing the current tension setting, so several arms can be dialled to the same level before any monitors go on. That is a detail aimed at someone fitting out an office, and it doubles as the tell for which model you own — green is the legacy M2.1, red is the M2 Pro that replaced it in North America in January 2026.

A steel spring has no gas to leak. It also has a fifteen-year warranty behind it, against ten for Ergotron’s gas arms. Whether it lasts longer in your room we genuinely cannot tell you — but Humanscale is willing to put five more years in writing, and warranties are priced by people with the failure data we lack.

No counterbalance at all

The third machine, and the one that gets unfairly marked down for an incomplete spec sheet.

VIVO’s V002 has no spring of any kind. The monitor mount clamps to a vertical pole, and you set the height by loosening the clamp, sliding it, and tightening it again. Friction and clamping force hold it. Gravity is not being cancelled — it is being resisted by a bolt.

Which means this arm has no minimum weight, and cannot have one. There is no spring pushing up, so there is nothing a light monitor could fail to overcome. A three-pound panel and a twenty-pound panel are held identically. When VIVO publishes a maximum and no minimum, the spec sheet is not incomplete — it is correct. There is no floor to disclose.

This is the one place on this site where a missing number earns no criticism. It also has a cost, and it is the obvious one: you have traded away movement. The V002 holds a height. It does not travel to a new one because you stood up, and repositioning it means a hex key rather than a fingertip.

How to choose, in one question

Ask whether the monitor needs to move.

If it lives at one height — fixed desk, one chair, one seating position — a non-counterbalanced arm does that job for less money, with no spring to sag, no minimum weight to check, and nothing to go quietly wrong in year four. Most people set a monitor once and never touch it again, and for them the cheapest mechanism is also the most robust one.

If it needs to move — you sit-stand, you share the desk, you pull the screen forward to read and push it back to type — you need a counterbalance, and that means accepting a minimum weight. So go and weigh your panel without its stand, because that is the number the arm actually sees, and it is the one thing that can make an otherwise perfect arm useless.

Then check the ends of the range against it. Under 7 lb rules out the LX. Under 4 rules out nearly everything. Under 20 rules out the HX, which sounds absurd for an arm rated to 42 lb and is exactly the trap that page exists to flag.

Once you know which mechanism you want, the single arm roundup prints both ends of every range, and VESA and weight ratings covers the other half of the question — whether the thing bolts to your monitor at all.