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A gas spring is sized by extended length, compressed length, stroke, and force, measured center-to-center between mounting points.
For the full breakdown, see our best 10 Inch Gas Spring 120 Pound guide.
A gas spring only a few millimeters too long can keep a lid from closing shut, while one that is too short will not hold the lid open. Labels fade over years of service, so most replacements start with knowing how to measure a gas spring the same way manufacturers do. You will need a tape measure, a pair of calipers, and about five minutes.
Measuring A Gas Spring: Start With Center-To-Center
Take every gas spring dimension from the center of one mounting point to the center of the other, never from the outside edges. An edge-to-edge reading includes both end fittings and can overshoot the true size by the full length of those fittings.
Have a helper support the lid, door, or hatch before you begin so it cannot slam down while you work. Then take three readings:
- Extended length: push the rod all the way out and measure center-to-center between the two mounting points.
- Compressed length: push the rod fully in and take the same center-to-center measurement again.
- Stroke: subtract the compressed length from the extended length. The result is how far the rod travels.
A worn spring can give a different reading on every attempt, so repeat each measurement twice. If the ends are threaded, measure thread tip to thread tip, but note that some size charts exclude the threads themselves from the length spec.
Write down all seven values below before you order; this is everything a supplier needs to match a replacement:
| Measurement | How To Take It |
|---|---|
| Extended length | Rod fully out, measured center-to-center between mounting points. |
| Compressed length | Rod fully in, measured center-to-center between mounting points. |
| Stroke | Extended length minus compressed length. |
| Rod diameter | Measure across the rod with calipers. Typical sizes: 6, 8, 10, or 14 mm. |
| Tube diameter | Measure across the cylinder with calipers. Typical sizes: 15, 18, 23, or 28 mm. |
| End fittings | Record both ends: threaded, eyelet, ball socket, welded end, or bracket. |
| Force rating | Read the stamped value on the tube; test near full extension if it is gone. |
Sizing Is Only Half The Match: Fittings And Threads
The two ends of a gas spring do not always match. A lid mount may use a ball socket while the frame side uses an eyelet, so note the fitting style on each end separately. Threaded ends add one more variable: you need the thread diameter and pitch, not just a visual match, because coarse and fine threads in the same size are not interchangeable.
One common mistake is ordering by extended length alone. Two springs can share an extended length but have different strokes, and the shorter-stroke unit will not open the lid far enough. Compare compressed length and stroke as a pair: compressed length plus stroke should always equal extended length, so if your numbers do not add up, re-measure before ordering anything.
What If The Force Rating Has Worn Off?
Force is normally stamped on the tube in pounds, newtons, or kilograms, and that printed value is the most reliable spec you can record. When it has worn off, you can measure the spring near full extension rather than guessing mid-travel.
Camloc’s technical guide labels the standard test positions P1 through P4 and defines P1 Static as the nominal force: compress the spring to about 10 mm from full extension, let it extend back to roughly 5 mm from full extension, hold it there for five seconds, then read the force.
Expect some variation between tests. Temperature, humidity, and whether the rod points up, down, or sideways all shift readings, and installation direction affects lubrication and seal design. If a spring gives noticeably different results on repeated attempts, it is likely worn out; replace it rather than trusting an average.
Once you have all seven numbers, matching a replacement is straightforward.
