A step-by-step guide to measuring gas struts and gas springs, understanding size codes, and selecting the correct force rating for your application.
Gas struts and gas springs are the same product — the terms are used interchangeably. This guide covers sizing for both.
To measure a gas strut correctly, you need four key dimensions. Measure with the strut fully extended and removed from the application where possible.
If you already know your measurements, jump straight to the Gas Strut Finder to find your matching part and buy online with next day delivery.
The total length of the strut when fully open - measured from the centre of one end fitting to the centre of the other.
This is the measurement most listed on product pages.
How far the rod travels from fully closed to fully open. Usually around 55–60% of the extended length for standard struts.
Compressed length = extended length minus stroke.
The diameter of the inner rod in millimetres. Common sizes are 6mm, 8mm, 10mm and 14mm.
This forms part of the size code — see the chart below.
The output force in Newtons (N), usually stamped or printed on the body of the strut.
Vari-Lift struts are supplied at max force and can be adjusted down.
The two numbers in the product code, e.g. 6-15 refer to the rod diameter and tube diameter in mm. The first number is the rod and the second is the tube body.
6-15 Range
6mm rod · 15mm tube
Light duty
8-18 Range
8mm rod · 18mm tube
Light–medium duty
10-23 Range
10mm rod · 23mm tube
Light duty
14-28 Range
14mm rod · 28mm tube
Heavy duty
Use the tables below to match your application's requirements to the correct gas strut size. First, identify the strut size by rod and tube diameter, then check that the force range is appropriate for your lid weight.
|
Size code |
Rod diameter |
Tube diameter |
Duty |
Typical applications |
|---|---|---|---|---|
|
6-15 |
6mm |
15mm |
Light |
Small cabinet doors, tool storage lids, small hatches |
|
8-18 |
8mm |
18mm |
Light–medium |
Campervans, furniture lids, motorbike panniers, garden storage boxes |
|
10-23 |
10mm |
23mm |
Medium |
Car bonnets, industrial access panels, tractor cab windows |
|
14-28 |
14mm |
28mm |
Heavy |
Heavy machinery covers, large industrial hatches and agricultural equipment |
Gas strut size chart: lid weight vs recommended strut size
Based on two struts supporting the lid. Weights are approximate — always allow for hinge position and lid geometry. Select force in 10 Newton intervals.
| Lid weight (kg) | Approx. force per strut (N) | Recommended size | Notes |
|---|---|---|---|
|
Up to 3 kg |
50–100 N |
6-15 |
Light-duty only; check mounting clearance |
|
3–6 kg |
100–200 N |
6-15 or 8-18 |
Consider 8-18 for longer stroke requirements |
|
6–10 kg |
200–350 N |
8-18 |
Most common size for DIY and van conversion use |
|
10–18 kg |
350–600 N |
8-18 or 10-23 |
Step up to 10-23 for higher force or longer stroke |
|
18–30 kg |
600–900 N |
10-23 |
Suitable for car bonnets and medium industrial lids |
|
30–55 kg |
900–1500 N |
10-23 or 14-28 |
Use 14-28 where higher rigidity is needed |
|
55 kg+ |
1500 N+ |
14-28 or custom |
Contact us to discuss your application |
Force range is determined by allowable pressure and rod buckling load. All adjustable variable force struts are supplied at maximum force and can be adjusted to your specific requirement.
|
Size code |
Minimum force |
Maximum force |
Force increments |
|---|---|---|---|
|
6-15 |
50 N |
400 N |
10 N intervals |
|
8-18 |
100 N |
650 N |
10 N intervals |
|
10-23 |
150 N |
1200 N |
10 N intervals |
|
14-28 |
300 N |
2500 N |
10 N intervals |
Enter the key dimensions from your existing strut to find matching stocked parts available for next day delivery. Rod diameter is selected first — compatible tube diameters are then shown automatically.
Measure these values directly from your existing gas strut. Use the tolerance fields if you can accept a close match rather than an exact size.
Force is optional — leave it blank to see all dimension matches. Material selection will filter to Black Nitrider or Stainless Steel only; choose Show both to see all stocked options side by side.
| Part number | Finish | Rod Ø | Tube Ø | Stroke | Extended length | Compressed length | Force (N) | Buy |
|---|---|---|---|---|---|---|---|---|
| Complete steps 1 and 2 to see your matches. | ||||||||
All dimensions (rod Ø, tube Ø, stroke, extended length, compressed length) are in millimetres.
The best dimension match is highlighted. Part numbers link directly to the product page. If you need help confirming the right strut for your application, contact our team — we're happy to help.
Download and complete our Gas Strut Sizing Questionnaire, then return it to our technical team. We'll recommend the correct strut for your specific setup.
↓ Download Gas Strut Sizing Form (PDF) or call us on 01623 788 400 or email: webenquiries@comdir.co.uk
If you're replacing a gas strut that's failed or lost pressure, follow these steps to identify a direct replacement.
Measure the extended length and stroke — Measure the old strut fully extended, centre of end fitting to centre of end fitting. Note the stroke length (how far the rod travels). If the old strut is collapsed, compressed length = extended length minus stroke.
Check the force rating — Look for a label or stamp on the body of the strut. It will show the force in Newtons (e.g. 500N). If the label is gone, use the lid weight table above to estimate the required force.
Measure the rod and tube diameter — Use calipers for accuracy. Match to the size code table above (e.g. 8mm rod, 18mm tube = size code 8-18).
Check the end fittings — The most common types are ball joints (clevis) and eyelets. Ensure the thread size and fitting type match your existing mounting brackets. View end fitting options →
Weigh the lid — If unsure about the force rating, weigh the lid to be supported (in kg) and cross-reference with Table 2 above. Allow for hinge placement — mounting closer to the hinge reduces the force required.
Mounting the strut closer to the hinge reduces the force required. The angle of operation affects how the strut extends — ensure it doesn't overextend or bind at the limits of travel.
Most applications use two struts, one on each side. The force tables above assume two struts. If using a single strut, double the force per strut required.
Gas struts lose a small amount of force in cold conditions. For outdoor or refrigerated applications, account for this or consider stainless steel struts for corrosive environments.
A strut with too much force will make the lid feel heavy to close; too little and it won't hold open. variable force struts allow adjustment after fitting — ideal if you're unsure about the exact force needed.
Cabinets and Furniture: Soft-close doors and hatches.
Car Bonnets and Boot Lids: Safe and secure opening and closing.
Motorbike Panniers: To hold the lid open securely while accessing storage.
Campervans: Pop-top roofs or storage compartments.
Industrial Equipment: Access panels and machine covers.
Bird Hides and Observation Points: Gas struts can lift and hold lids or shutters open, making them silent and easy to use for nature enthusiasts.
Animal Enclosures: Used for hatches or lids in zoos, farms and wildlife parks.
Garden Storage Boxes: Gas struts ensure smooth operation of heavy lids for outdoor storage
Toolboxes and Workstations: Lid support for safe and easy access.
Medical Equipment: Used for adjustable hospital beds, trolleys and operating tables.
Tractor Cabs: Support for windows or access panels.
Aviation Applications: Access panels or storage compartments in small aircraft.
Available in stock for online ordering with next-day delivery.
Open the lid or hatch to fully extend the strut. Measure from the centre of the end fitting at the body end to the centre of the end fitting at the rod end - this is the extended length.
For the stroke, measure the length of exposed rod (the shiny section visible outside the body). If you can't easily access the fittings, measure body-to-body and add roughly 10–15mm per end fitting to account for the mounting centres.
The two numbers refer to the rod diameter and tube diameter in millimetres. So 8-18 means an 8mm rod inside an 18mm tube.
The rod diameter affects the maximum force the strut can handle before buckling, and the tube diameter determines the overall body size.
Common sizes are 6-15 (light duty), 8-18 (light-medium), 10-23 (medium) and 14-28 (heavy).
Stroke length is the distance the rod travels from fully compressed (closed) to fully extended (open). It determines how far your lid or hatch can open. For most standard gas struts, stroke length is roughly 55–60% of the extended length. Compressed length = extended length minus stroke length.
A useful starting point is: weigh the lid in kg, multiply by 10 (to approximate Newtons), then divide by two if using two struts. However, this doesn't account for hinge position or lid geometry. For a more accurate calculation, use our Gas Strut Sizing Form or contact our technical team. Our Vari-Lift struts are supplied at maximum force and can be adjusted down after fitting, which takes the guesswork out of it.
Yes, provided the force rating and mounting points are compatible. The end fittings (ball joints, eyelets) must suit your existing brackets, and the compressed length must fit within your available space when the lid is closed. Matching the original extended length and stroke as closely as possible is recommended. If switching to a different size code (e.g. from 6-15 to 8-18), check that the body diameter will clear any surrounding panels or frames.
A standard gas strut is supplied at a fixed force and cannot be adjusted. A Vari-Lift gas strut is supplied at maximum force and can be adjusted downwards on-site using a release tool - allowing you to dial in the exact force your application needs without ordering multiple struts. All our standard gas struts and Stainless Steel ranges are Vari-Lift.
They are the same product. "Gas strut" is the more common term in UK automotive, DIY and trade contexts. "Gas spring" is widely used in industrial, engineering and international applications. Both terms describe a sealed cylinder containing compressed nitrogen gas and oil, which provides a controlled force to support or lift a load.
If the force is too high, the lid will be very hard to close and may place excessive stress on hinges and mountings. If the force is too low, the strut won't hold the lid open, particularly dangerous for heavy lids. Incorrect extended or stroke length can cause the strut to bind, overextend, or fail to fit within the available space when closed.
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