5 Key Measurements for Gas Spring Selection
Most incorrect gas spring orders are caused not by the product itself, but by five basic values being missing or wrongly defined. In this article we go through those five values one by one — together with the measurement mistakes we see most often in the field.
1. S — Stroke
The distance the rod travels between the extended and compressed positions. How many millimetres your flap or lid needs to move determines the stroke; however, the stroke should never be sized to match the full end-to-end clearance. Using the gas spring's entire travel as a mechanical end stop shortens its life — wherever possible, physical stops in the application should limit the movement.
2. L1 — Extended Length
The distance between the two mounting points with the gas spring fully extended: measured hole centre to hole centre on eyelet end fittings, and from ball centre to ball centre on ball-studs. The most common mistake is measuring the tube body and leaving the end fittings out of the equation — the same body yields an L1 that differs by 30–80 mm depending on the end fittings selected.
3. L2 — Compressed Length
The centre-to-centre distance in the fully compressed position, which defines your installation envelope. L2 is the stroke plus the body's dead length; dead length grows as the size class gets larger. In tight installation spaces, verify L2 first — we have heard "we thought it would fit" far too many times.
4. F1 — Force
The extension force the gas spring exerts near the fully extended position, measured at 20 °C. By the nature of nitrogen, force changes with temperature: every 10 °C shifts F1 by roughly 3.3%. A hatch operating outdoors in winter gets noticeably less support than the force you measured in summer — always specify the application's temperature range.
5. Progression — The Force Increase Ratio
Force progression indicates how much the force rises as the gas spring compresses. At the same rod diameter, a larger tube means lower progression: in sensitive applications where "stiffening" towards the end of travel is unwanted (medical, furniture), low-progression size groups are preferred. An order placed without progression ever being discussed usually comes back with the complaint "it gets hard to push near the end".
· When replacing an existing gas spring, read the label; if the label is worn off, measure L1 in the extended position, not compressed.
· Do not describe the force as "it felt about this much when I pushed by hand" — lid weight, centre of gravity and hinge distance call for a proper calculation.
· In twin gas spring applications the total force is split between the two units; if one side fails, always replace them as a pair.
Once these five values are pinned down, your gas spring definition fits on a single line: for example GL8/18-200-472-400N-C02/C02. And if you do not know your values, that is fine too — our configurator asks step by step, recommends the size group and generates the part code.