Gas Spring Size Chart: Extended Length, Stroke, Diameter and Force Explained

A maintenance buyer sends over a photo of a worn chair cylinder and one question: which size do I order? The answer almost always sits in four numbers, and only two of them really need a caliper. A gas spring size chart is a matching tool, not a shopping list — you read it from your measurements, never the other way around.

What follows is the working sequence we use with customers: the four defining numbers, a reference chart of standard combinations, the measurement routine, the variables that quietly break a clean match, and the selection logic that keeps a replacement order from coming back.

The Four Numbers That Define a Gas Spring Size

Every column in a size chart is a restatement of one of these four values. Get all four right and the brackets, sockets and levers usually follow without a second thought.

Get one of the four wrong and the symptom is predictable: too short a stroke and the mechanism will not close, too high a force and the user cannot pull the lid down, too small a body and the spring bends or the force cap is unreachable.

A Reference Gas Spring Size Chart

Tube and rod combinations are standardised because the tooling behind them is expensive. That is why a handful of sizes cover most of the market. The ranges below are typical for industrial, seating and cabinet applications, with forces quoted at 20 °C.

Office chair lift cylinders sit outside this logic. They are telescopic units specified by travel stroke, outer tube diameter and load class rather than extended length, and they mount through a standard taper. If you are replacing one, measure the travel with the chair at its lowest and highest setting rather than trying to match a chart row.

Standard Height Heavy Duty Office Chair Gas Lift CylindersThese 300–500 N office chair gas lift cylinders suit heavy-duty seating and come in multiple stroke sizes for replacements; load class affects lever feel.View Product →

Chair cylinders also behave differently in one practical sense: a heavier-rated unit does not simply lift more, it changes the feel of the lever, so the load class matters as much as the stroke.

How to Measure Before You Buy

Five measurements, ten minutes, one caliper and a tape. This is the routine that removes most ordering errors.

1. Extend the spring fully and measure centre-to-centre between mounting holes. Write this down as your extended length.
2. Compress it against a firm surface until it bottoms out on the internal stop, then measure again. Extended minus compressed is the stroke.
3. Measure the outer tube diameter over the middle of the body and the rod diameter just behind the seal. Both are usually nominal values, so 21.8 mm means a 22 mm tube.
4. Read the force marking from the old unit. It is often printed in newtons, sometimes in pounds, and occasionally encoded in a colour band on the rod.
5. Identify the end fittings — ball socket, eyelet, threaded stud or bracket. A correct length with the wrong socket is still the wrong spring.

Substitution rules are more forgiving than most buyers expect. Extended length can deviate if the mounting slots allow adjustment, but stroke should never be shorter than the original. Force can usually move by ±10% without a complaint, and up to 20% upward on a lid that has always felt heavy. If your application uses a non-standard socket or stud, it is worth reviewing the common end mounting methods for gas springs before you commit to a chart row.

Hidden Variables That Break a Clean Chart Match

Two springs with identical labels can behave very differently on the same machine. The dominant variable is temperature, because the force comes from a compressed nitrogen charge and that charge follows gas law behaviour: roughly 3% per 10 °C around room temperature.

Relative force against a 20 °C rating, derived from the nitrogen charge behaving as an ideal gas. A spring that holds perfectly in a showroom can feel weak on a loading dock in January and stiff enough to resist closing in a summer workshop.

• Damping: an internal oil damper slows the last few millimetres of travel, which is why the rated point is quoted before the end of the extension, not at full extension.
• Mounting angle: a spring that does not act perpendicular to the hinge converts part of its force into a sideways load, so the effective lift drops even though the gauge reads correctly.
• Geometry: two springs on one lid halve the load each but double the cumulative error when their forces differ.
• Time: gradual gas loss across years of cycles is normal, so a replacement of the same nominal force usually feels stronger than the tired unit it replaces.

Where Each Size Class Ends Up

Demand clusters around a few size classes, and knowing where your application sits helps you sanity-check a chart row before you order.

Seating is where volume lives, and it is also where the sizing tolerances are tightest, because a stroke that is 10 mm short is instantly obvious to the person sitting on the chair. Bar stools and similar adjustable seats sit in the middle of that band and often use a heavier charge than the frame suggests, because the seat has to hold at height under an uneven load.

ADF-243 Bar Stool Gas Springs, 120 mm TravelThe ADF-243 series fits bar stools and similar seating, with 120 mm travel, 10/20 mm connection options, and damped quiet height adjustment.View Product →

Industrial and automotive panels tolerate wider length windows because the mounting brackets usually include slotted holes, but they demand far better corrosion protection and far more attention to the force at temperature extremes.

Selection Guide and the Cost of a Wrong Size

A wrong spring rarely fails loudly. It returns as a complaint, a warranty claim or a line stoppage, and by then the freight, handling and labour cost far exceed the part price. The sequence below keeps that number small.

Lockable Gas Springs for Office and Hairdressing ChairsFor position-holding chair and bed adjustment, this lockable gas spring locks at any point and supports 450–1200 N for seating and hospital beds.View Product →

The arithmetic is simple. One measured sample and a signed drawing cost a few hours; a returned batch of 500 units costs the part price several times over in reverse freight, re-inspection and the production window you lose while waiting for the replacement.

Maintenance and Compliance Notes

Gas springs are pressure vessels, even the small ones. They cannot be repaired, adjusted or refilled in the field, and opening one is dangerous. When a unit loses force, it is replaced, not serviced.

• Store springs with the rod down and keep them out of direct sun. Solvent or paint on the rod damages the seal and shortens service life.
• For disposal, depressurise the cylinder in a controlled way before scrapping, following your local pressure-vessel guidance.
• Ask for the force test record at 20 °C, a dimensional report and salt spray results for the plating. A documented 48 to 96 hours of neutral salt spray is a reasonable benchmark for exterior use.
• Where the application is regulated — vehicle interiors, medical equipment, lifting equipment — confirm the applicable standard and the cycle life before you approve the size.

Changzhou Andefu Gas Spring builds gas springs and cylinders to customer drawings or samples, with in-process inspection on every operation and testing equipment in house. The plant covers 6,000 square metres with 15 production lines, and sits within easy reach of the Nantong and Shanghai ports, which keeps export shipments predictable for buyers matching a chart row to a production drawing. If your measurements fall between two standard sizes, send the drawing or the original sample through our contact page and we will quote the closest custom build rather than force the nearest catalogue number.