A monitor arm is usually sold as a way to clear desk space. That is true, and on a sit-stand desk it is the least interesting of the three things it does.
Why it matters more on a sit-stand desk
1. It decouples screen height from desk height
Your elbows set the desk height. Your eyes set the screen height. On a monitor stand those two are locked together, so setting the desk correctly for your arms usually puts the screen too low — and you spend the day looking down. An Ergotron LX publishes about 13" of lift, which is enough to break that dependency entirely.
For tall users this is the difference between a desk that works and one that gives you neck pain — see the tall-user roundup.
2. It reduces the wobble you actually feel
Monitors on tall stands sit high above the desk surface and act as a lever: mass far from the pivot means a small deck movement becomes a large, visible screen movement. Clamping the screens to the desk edge lowers the center of mass and anchors it. The full explanation, and when it does not help.
3. It frees the depth a converter would have eaten
A monitor stand occupies 8 to 10 inches of desk depth. On a 24-inch desk that is a third of your working area.
The specs that decide it
|
| Weight capacity | 26 lb (11.8 kg) | 7 to 25 lb (3.2 to 11.3 kg) per LX arm |
| Lift range | 33 cm (about 13") | Reduced by up to 4.5" with monitors over 20 lb, for a total of 8.5" |
| Construction | Aluminum and steel | Aluminum and steel |
| Mounting | Clamp or grommet included | Single clamp point for both screens |
| Warranty | 10 years | 10 years |
The published note nobody else prints
Ergotron states that with monitors over 20 lb, the LX Dual's vertical range of motion may be reduced by up to 4.5", for a total height range of 8.5". That is a maker publishing a limitation of its own product, and it is exactly the figure that decides whether a dual arm works for you. If you run heavy screens and need full travel, two single arms are the better answer.
Check your monitor's weight without its factory stand — that is what the arm carries, and it is often 4 to 8 lb less than the shipping weight you find first.
Constant-force versus gas spring
This is the difference between an arm that holds its height in year four and one that slowly droops.
- Constant-force spring — a mechanical spring delivering even force across the travel. What Ergotron uses on the LX, and the reason it holds position.
- Gas spring — a sealed gas cylinder. Cheaper, and the seal is a consumable. The classic failure is a monitor that sinks an inch overnight.
Either way, set the tension properly on day one, with the monitor mounted. Ergotron's instructions bury this step, and an arm with the tension wrong feels like a broken arm.
Mounting on a sit-stand top
Two checks specific to this site's readers, and both are easy to get wrong.
- Desktop thickness. A clamp on a thin sit-stand top can flex. Below about 0.6" we would not clamp an arm at all — and a dual arm puts two monitors' worth of leverage through one point.
- Frame capacity. An arm plus monitors is 25 to 45 lb added to your desk. Not a problem on a 355 lb frame; worth counting on a 200 lb one. Run the numbers.
A grommet mount is stronger than a clamp if your top has a hole or you are willing to drill one. On a desk you plan to keep for fifteen years, drilling it is less drastic than it sounds.
If you are not sure your desk can take a clamped arm, the arm-versus-stand comparison runs the four checks that decide it, and the accessory buying order explains why an arm is the first thing we would add to a sit-stand desk.
