Gas Strut Size Guide: Compression and Extension Explained

Choosing the correct size gas strut is essential for ensuring proper functionality and safety in various applications, from car boots and bonnets to furniture and industrial equipment. This guide provides a comprehensive overview of gas strut sizing, focusing on compression and extension lengths, and how to accurately measure for replacements. Refer to the Gas Spring Force Calculator to calculate the correct size for your application.

Why is Gas Strut Size Important?

Incorrectly sized gas struts can lead to several problems:

Failure to Support Weight: A gas strut that is too weak will not be able to support the intended weight, causing lids, doors, or panels to droop or fall shut.
Overextension: A strut that is too long may overextend the mechanism, potentially causing damage to the hinge points or the strut itself.
Binding: A strut with incorrect compression can bind or prevent the mechanism from closing properly.
Safety Issues: In automotive or industrial applications, incorrect strut sizing can pose safety hazards.

How do I know my gas strut needs replacing?

A failing gas strut exhibits several telltale signs. The most common symptom is a loss of lifting assistance, causing the supported object to sag or fall. Other indicators include visible damage, such as dents or leaks, and unusual noises during operation. Refer to the Gas Spring Force Calculator tool to ensure proper sizing for your replacement.

Symptoms of a Failing Gas Strut

Here are the common symptoms that indicate a gas strut needs replacement:

Loss of Lifting Assistance: The most obvious sign is the inability of the strut to hold up the intended weight.
Sagging or Drooping: The supported object (e.g., car boot, bonnet) droops or falls shut without assistance.
Visible Damage: Dents, bends, or leaks on the strut body.
Unusual Noises: Squeaking, hissing, or popping sounds during operation.
Slow or Jerky Movement: The strut extends or compresses unevenly or slowly.

What size strut does a [car] need?

Gas strut size depends on the application. Critical measurements include extended length (eye-to-eye), stroke length (difference between extended and compressed), and force rating in Newtons (N). Always check the manufacturer’s recommendations or the original strut’s markings for accurate replacement. The Gas Spring Force Calculator is helpful in determining the size for your specific application. The table below shows common sizes:

Gas Strut Dimensions

Dimension	Description	Importance
Extended Length	The distance between the end fittings when the strut is fully extended.	Crucial for ensuring the mechanism reaches its full range of motion.
Compressed Length	The distance between the end fittings when the strut is fully compressed.	Determines the minimum space required for the mechanism to close fully.
Stroke Length	The difference between the extended and compressed lengths.	Determines the range of motion provided by the strut.
Rod Diameter	The diameter of the piston rod.	Affects the strut’s force capacity and durability.
Cylinder Diameter	The diameter of the strut’s cylinder.	Also affects the force capacity.
End Fittings	The type of fittings at each end of the strut (e.g., eyelets, ball joints, threaded studs).	Must match the mounting points on the application.

Understanding Key Gas Strut Dimensions

When determining the size of a gas strut, it is crucial to understand the following dimensions:

Extended Length

The extended length is the overall length of the gas strut when it is fully extended. This measurement is taken from the center of one end fitting to the center of the other. The extended length dictates the maximum reach of the strut and ensures the supported lid, door, or panel opens to the desired angle.

Incorrect extended length can result in overextension, placing undue stress on hinges and mounting points. For help with calculation, use our Gas Spring Force Calculator.

Compressed Length

The compressed length is the overall length of the gas strut when it is fully compressed. This measurement is also taken from the center of one end fitting to the center of the other. The compressed length determines the minimum space required for the mechanism to close fully.

If the compressed length is too long, the mechanism may not close completely or may require excessive force to close. It’s important to consider the mounting location to ensure there are no obstructions, as seen in automotive applications.

Stroke Length

The stroke length is the difference between the extended length and the compressed length. It represents the total distance the piston rod travels during the strut’s operation. The stroke length determines the range of motion provided by the strut.

Ensuring the correct stroke length is critical for smooth and controlled movement. Too short a stroke will limit the opening angle, while too long a stroke can cause binding or damage. The correct stroke length is especially important in furniture applications.

How to Measure a Gas Strut for Replacement

Accurate measurement is essential when replacing a gas strut. Follow these steps to ensure you select the correct replacement size:

Step 1: Gather Your Tools

Measuring Tape or Ruler
Pencil and Paper
Safety Glasses

Step 2: Safely Remove the Old Gas Strut

If possible, have an assistant support the lid or panel to prevent it from falling.
Use a flathead screwdriver or a similar tool to carefully detach the end fittings from their mounting points.
If the strut is damaged or heavily corroded, wear safety glasses to protect your eyes.

Step 3: Measure the Extended Length

Fully extend the old gas strut. If it is damaged and cannot fully extend, try to extend it as much as possible without forcing it.
Measure the distance from the center of one end fitting to the center of the other.
Record this measurement as the extended length.

Step 4: Measure the Compressed Length

Fully compress the old gas strut. If it cannot be compressed, estimate the compressed length based on the design of the mechanism.
Measure the distance from the center of one end fitting to the center of the other.
Record this measurement as the compressed length.

Step 5: Calculate the Stroke Length

Subtract the compressed length from the extended length.
The result is the stroke length.
Record this measurement.

Step 6: Identify the End Fittings

Note the type of end fittings on the old gas strut. Common types include:

Eyelets
Ball Joints
Threaded Studs

Step 7: Check the Force Rating

Examine the body of the old gas strut for a force rating, usually expressed in Newtons (N). This indicates the force the strut exerts when extending.

How to Select the Correct Replacement Gas Strut

With your measurements in hand, follow these steps to select the correct replacement gas strut:

Match the extended length, compressed length, and stroke length as closely as possible to the original strut.
Ensure the end fittings are compatible with the mounting points on your application.
Select a replacement strut with the same or slightly higher force rating as the original. If you’re unsure, it’s better to err on the side of a slightly stronger strut. This is important for various caravan and marine usages.
Consider factors such as operating temperature, environment, and cycle life for demanding applications.

Where can I buy one?

Gas struts are available from various suppliers, including automotive parts stores, hardware stores, and online retailers. When purchasing, be sure to provide the measurements and specifications you gathered to ensure you receive the correct replacement.

Check out our range of gas struts on WooCommerce. Please check our fitment guide before ordering.

For bespoke or bulk orders, contact our industrial team.

Gas Strut Size Guide: Compression and Extension Explained