How Do I Figure Out What Gas Spring I Need? Complete Specification Guide
Understanding the Three Essential Specifications
Capsule: Every gas spring is defined by three measurements: extended length, compressed length, and force rating in Newtons. Get these right and you’ll specify the correct strut.
Before you can order a replacement or new gas spring, you need to understand what makes each one unique. Unlike a static spring, a gas spring combines a piston rod, sealed cylinder, and pressurised nitrogen gas. The three critical specifications that define any gas spring are:
- Extended length: The total distance from the eye or mounting point at one end to the eye or mounting point at the other, when the strut is fully extended (at rest, no load applied)
- Compressed length: The shortest distance the strut can be compressed to under full load
- Force rating: The pushing force, measured in Newtons (N), that the strut generates when compressed
The stroke length—the distance the piston rod travels—is calculated by subtracting compressed length from extended length. This determines how much vertical or horizontal movement the application allows.
Understanding these three dimensions is the foundation of gas spring specification. Without them, you’ll either order the wrong part or waste time guessing.
How to Measure Extended and Compressed Length
Capsule: Extended length is measured from eye-to-eye when the strut is fully open. Compressed length is measured from eye-to-eye when the rod is pushed fully into the cylinder. Use a ruler or calliper for accuracy to the nearest 5mm.
If you’re replacing an existing gas spring, measuring the current one is the fastest route to specification. Here’s the step-by-step method:
Measuring Extended Length (Rod Fully Out)
- Lay the gas strut on a flat surface or hold it horizontally
- Position a ruler or measuring tape along the length of the strut
- Measure from the centre of the eye hole (or mounting point) at one end to the centre of the eye hole at the other end
- Record this measurement in millimetres. Round to the nearest 5mm if your ruler isn’t precise
- This is your extended length
Measuring Compressed Length (Rod Fully In)
- Hold the strut vertically or lay it on a workbench
- Apply firm downward pressure to compress the rod fully into the cylinder
- You’ll feel resistance—this is the gas pressure inside. Push through it firmly until the rod stops moving
- Measure from eye-to-eye again, just as you did for extended length
- Record this measurement. This is your compressed length
Calculating Stroke Length
Stroke = Extended Length − Compressed Length
For example, if extended length is 400mm and compressed length is 250mm, stroke = 150mm. This means the strut can move 150mm vertically (or in any direction, depending on how it’s mounted).
Reading the Force Rating from Your Current Strut
Capsule: The force rating in Newtons is printed on the side of the gas strut cylinder. If the label is faded or missing, use our Force Calculator to determine the correct force for your application.
If you have an existing gas spring you’re replacing, the force rating should be printed directly on the cylinder barrel. Look for a label or stamped text that reads:
- “400N” or “400 N”
- “50 lbf” (pounds-force, common on US imports)
- Sometimes printed as “Gas Spring 400N” or similar
The force is always in Newtons, regardless of the strut’s origin. If you find an older strut marked in pounds-force, convert it: 1 lbf = approximately 4.45 Newtons. A 90 lbf strut is roughly 400N.
Once you’ve identified the force rating, you know two of your three specifications. Now you need to confirm the force is actually correct for your application.
Using the Force Calculator to Verify or Determine Force
Capsule: The Force Calculator takes your lid/panel weight, hinge distance, and mounting geometry to recommend the correct Newton force. Use it when replacing an unknown strut or designing a new application.
If you don’t have an existing strut to measure, or if the current one isn’t holding the lid properly, use the Gas Spring Force Calculator to determine the correct force for your specific situation.
To use the calculator, you’ll need:
- Weight of the lid or panel: In kilograms or pounds. Weigh it on a bathroom scale or estimate based on material and size
- Distance from hinge to strut attachment point: Measure in millimetres or inches. This is the horizontal distance along the lid
- Mounting angle: Is the strut vertical, horizontal, or at an angle? Most lid applications are vertical or near-vertical
- Desired support: Should the lid float effortlessly (full support) or require some manual effort to open (partial support)?
The calculator outputs a force range—for example, “400–450N recommended.” Choose the lower end if you want easy opening; the upper end if you want positive hold-up.
Identifying the End Fitting Type
Capsule: Gas springs come with five main end fitting types: eye (loop), stud (threaded rod), clevis, ball socket, or trunnion. Match the existing mounting holes on your application.
The three length measurements are half the story. The other half is how the strut attaches to your application. Gas springs use five primary end fitting types:
Eye-to-Eye (Most Common)
Both ends have circular eyelets. A pin or bolt passes through each eye to create a pivot. Common on car boots, furniture lids, and machinery guards.
Stud-to-Eye (Rod End)
One end has a threaded rod (stud) that screws into an existing hole. The other end has an eye. Found on some overhead cabinet applications.
Clevis (U-Bracket)
One or both ends feature a clevis fork—a U-shaped bracket with holes on either side. Provides a wider mounting surface for angled applications.
Ball Socket
One or both ends have a ball joint that allows rotation in any direction. Used on tractor cabs, industrial machinery, and applications with changing angles.
Trunnion (Fixed Mount)
One end is a solid tang welded to the cylinder; the other is an eye or stud. Less common, usually for OEM or specialist applications.
To identify your end fitting, photograph both ends of your current strut or measure the hole diameter and spacing. When ordering, specify both end types—for example, “eye-to-eye” or “stud-to-eye.”
Confirming Material Grade and Temperature Range
Capsule: Standard gas springs work at −30°C to +80°C in mild steel. Marine applications require 316 stainless steel. Industrial applications may need high-temperature or low-temperature variants.
For most automotive, furniture, and general applications, a standard mild steel gas spring with a −30°C to +80°C operating range is sufficient. However, check your environment:
- Marine or coastal exposure: Use 316 stainless steel. Standard mild steel will rust within months in salt spray
- High-temperature environments: Furnace doors, industrial ovens—use high-temperature gas springs (up to 150°C)
- Extreme cold: Arctic or deep-freeze storage—specify low-temperature variants
- Corrosive chemicals: Food processing, chemical plants—verify coating or material compatibility with your installer
If your application is indoors, unheated, and at sea level, standard mild steel is fine. For anything exposed outdoors or in moisture-rich environments, 316 stainless steel is worth the investment to avoid premature failure.
Matching to Your Specific Application
Capsule: Once you have extended length, compressed length, force, end fittings, and material grade, cross-reference your application type to confirm fitment. Automotive and furniture applications have specific compatibility rules.
Now that you have your specifications, match them to your application:
Automotive Applications
If you’re replacing a car boot, bonnet, or hatchback strut, use the Gas Strut Replacement Finder to cross-reference your vehicle make and model. This ensures you don’t order a strut that’s close but incompatible with your car’s hinge geometry.
Furniture and Cabinet Applications
Measure your cabinet’s hinge spacing and lid weight. Use the Force Calculator. Then verify the eye-to-eye length fits between your existing pivot points with 10–20mm clearance on each side. Too long and it won’t fit; too short and the angles will be extreme.
Marine and Outdoor Applications
Specify 316 stainless steel. Verify the compressed length fits your hatch cavity when fully closed. Check that extended length doesn’t exceed the open space when the hatch is fully open.
Industrial and Machinery Applications
For machine guards, access panels, or specialised equipment, provide the full specification to your supplier: extended length, compressed length, force, end fittings, and environmental conditions. Industrial applications often require cycle life certification (50,000 or 100,000 cycles).
Where to Buy Once You Know Your Specification
Capsule: Provide your complete specification—extended length, compressed length, force in Newtons, end fittings, and material—to your supplier. They’ll match it to a compatible part or order a custom build if needed.
Once you have your complete specification, you’re ready to order. Whether you’re sourcing a replacement for an existing strut or specifying a new one, provide your supplier with:
- Extended length (mm)
- Compressed length (mm)
- Force rating (Newtons)
- End fitting types (e.g., eye-to-eye)
- Material grade (mild steel, 316 stainless, etc.)
- Your application (car boot, furniture lid, industrial guard, etc.)
For automotive applications, many retailers offer fitment tools where you enter your vehicle registration and they suggest the correct part. For furniture and marine applications, use the Gas Strut Compatibility Checker to verify your order matches your exact setup.
When ordering through Aritech Gas Springs, you can use the complete specification or provide your vehicle make and model for instant fitment confirmation.
Troubleshooting Specification Mismatches
Capsule: If your new strut is too strong, it will lift the lid too easily or slam it open. If too weak, the lid won’t stay up. Measure again and use the Force Calculator to determine the correct force for the next replacement.
If you’ve ordered a strut and it’s not performing as expected, the issue is usually force-related:
- Too strong: The lid pops open with minimal pressure or flies up violently. Solution: order a lower Newton rating (200N instead of 300N, for example)
- Too weak: The lid won’t stay open or closes slowly. Solution: order a higher Newton rating
- Wrong length: The strut bottoms out (compressed length is too short) or leaves a large gap when the lid is closed (extended length is too long). Solution: re-measure and order the correct length
- End fitting mismatch: The strut won’t bolt to your pivot points. Solution: confirm end fitting types with your application and order again
Use the Force Calculator again after the first fitting to fine-tune your next order if needed.
Summary: Your Gas Spring Specification Checklist
Before ordering, confirm you have all five components of a complete specification:
- ✓ Extended length (eye-to-eye, fully open): _____ mm
- ✓ Compressed length (eye-to-eye, fully closed): _____ mm
- ✓ Force rating: _____ Newtons (use Force Calculator if unsure)
- ✓ End fitting types: _____ (eye, stud, clevis, ball socket)
- ✓ Material and environment: _____ (mild steel, 316 stainless, high-temp, etc.)
Once these five elements are confirmed, you’re ready to order with confidence. Your replacement or new gas spring will fit correctly and perform as intended.