Retrofitting Gas Struts — Step-by-Step Guide

A gas strut, also known as a gas spring, assists with opening cabinet flaps using compressed gas and holds them open automatically.

Retrofitting these fittings is a common task in furniture making and interior joinery. Whether in the kitchen above the microwave, in the living room, or in the office, a properly adjusted flap significantly improves furniture ergonomics. This guide is aimed at fitters and experienced DIY enthusiasts looking to calculate, position, and install flap fittings correctly.

Installation requires precise measuring and a basic understanding of leverage. The time required for a standard flap with two struts is approximately 30 to 45 minutes.

Before Installation: Calculating the Correct Force in Newtons

The most common mistake when installing a gas strut is selecting the incorrect force rating. This is specified in Newtons (N). If the strut is too weak, the flap will drop shut. If it is too strong, closing the cabinet door will require excessive effort, putting undue strain on the hinges.

The required force depends on the weight of the flap (including the handle) and its height. As a rule of thumb for standard furniture flaps (opening angle 90°): 1 kg of flap weight corresponds to approximately 10 N of holding force.

Example: If an MDF flap (thickness 19 mm) with a metal handle weighs exactly 4.5 kg, you require a total force of around 45 N. Because flaps with a width of 400 mm or more should always use two struts (to prevent door warping), divide this value by two. In practice, you would choose two struts rated at 50 N or 60 N each to provide a slight safety margin.

For solid wood fronts or particularly large units, choose gas struts for heavy flaps that provide ratings of 120 N, 150 N, or more.

Required Tools and Materials

For a professional installation, you will need the following tools. Have everything within reach before you start measuring.

• Tape measure or folding rule
• Try square (for exact 90-degree marking)
• Pencil
• Bradawl
• Cordless screwdriver
• Wood drill bit (Ø 2 mm for pilot holes)
• Pozi screwdriver or matching bit (usually PZ2 for standard chipboard screws)
• Two gas struts including mounting plates (carcase and front fixings)
• Fixing screws (typically Ø 3.5 mm x 16 mm or 4 mm x 16 mm, countersunk)

Step-by-Step Installation Guide

Exact mounting positions (drilling templates) vary depending on the manufacturer, strut length, and required opening angle (usually 75°, 90°, or 110°). Always refer to the specific manufacturer datasheet. The following guide describes the procedure for a typical strut with a 268 mm overall length for a 90° opening angle.

Step 1: Measuring the Carcase

Installation begins on the inside side wall of the cabinet (the carcase).

1. Measure inward from the front edge of the carcase (excluding the front door). A typical dimension for the front screw of the carcase bracket is 25 mm.
2. Measure vertically downwards from the inside top edge of the cabinet (below the top panel). For a 90-degree opening angle, this dimension is often 250 mm to 260 mm.
3. Mark the intersection of these two lines with a pencil.
4. Position the carcase mounting plate (usually a round or oval bracket with a ball stud) on this mark and mark the screw holes.

Step 2: Drilling Pilot Holes and Fitting the Carcase Bracket

Use the bradawl to make a light indent at the marked points so the drill bit does not slip. Drill pilot holes using the 2 mm wood drill bit to a maximum depth of 5 mm. This prevents the chipboard or melamine coating from splitting. Secure the mounting plate with the cordless screwdriver and appropriate screws (e.g. 3.5 mm x 16 mm). Take care not to overtighten the screws.

Step 3: Measuring the Flap

Next, install the matching bracket on the cabinet flap.

1. Measure inward from the outer side edge of the flap. This measurement must match the carcase bracket distance (e.g. 25 mm minus the reveal).
2. Measure downward from the edge where the hinges are located (usually the top edge) towards the handle side. A typical dimension for the front bracket is 90 mm to 100 mm.
3. Mark the position, mark the holes with the bradawl, and pre-drill lightly. Take extreme care not to drill through the front. Ideally, use a depth stop on the drill bit.
4. Secure the front mounting plate with screws.

Step 4: Clipping the Strut in Place

Gas struts are generally clipped onto the installed ball studs without tools. A key technical rule applies here, similar to a car boot strut: the thicker section (the cylinder) must point upwards when closed, and the thinner section (the piston rod) must point downwards. This ensures the seal inside the cylinder remains permanently lubricated by internal oil, preserving the life of the fitting. First, push the cylinder socket onto the stud on the carcase until it clicks audibly into place. Then open the flap and press the piston rod socket onto the front bracket stud.

Step 5: Functional Test and Fine Adjustment

Open and close the flap several times. It should move smoothly upwards and stop securely in the end position without tearing at the hinges. Direct adjustment of the pressure force is not possible on standard struts. If the angle is not perfectly aligned, some front brackets feature slotted holes to allow fine adjustments of 2 mm to 3 mm.

Visual Integration into Furniture

While technical functionality is the priority, interior appearance also matters, especially in open-plan designs or frequently used units like a lowboard for TV. Match the hardware colour to the carcase finish. For white cabinets, a gas strut white is ideal, while on dark wood decors or anthracite boards, a gas strut black blends in seamlessly. The industry standard remains the gas strut silver, which matches universally with metal concealed hinges.

Common Mistakes and Expert Tips

• Incorrect hinges: Gas struts are not hinges. You must use cabinet hinges to secure the flap to the unit. Use standard concealed hinges without an integrated self-closing spring, as a sprung hinge will fight against the gas strut mechanism.
• Fitting only one strut: Do not cut corners here. Always install two struts (left and right) on flaps measuring 400 mm wide or more. A single strut applies asymmetric force, causing the flap to warp over time, close unevenly, and strain the hinges on the unsupported side.
• Confusing fitting types: A gas strut opens actively. If you only require a mechanism to hold a flap open at a specific angle without providing lifting power, you need a mechanical flap stay.
• Incorrect orientation: As outlined in Step 4, installing the strut with the piston rod pointing upwards causes seals to dry out and wear quickly. The strut will lose its gas and cease to function.

FAQ – Frequently Asked Questions

Can I repair a faulty gas strut? No. The cylinders are under high pressure. Opening them is dangerous and not technically feasible. Defective struts (recognisable by lost holding force or an oily film on the piston rod) must be fully replaced.

How do I find a replacement for an old strut? Check the number printed on the old cylinder (e.g. "80N" or "0080 N"). Measure the total extended length from ball socket centre to ball socket centre (usually between 240 mm and 270 mm). Purchase a replacement with the matching Newton rating and length. The existing mounting plates can often remain on the wood if the ball stud diameter matches.

Are gas struts suitable for humid rooms? Yes, standard models can be used in kitchens (e.g. above a wall cabinet dish drainer) or bathrooms. Ensure the surface coating remains undamaged to prevent rust on the cylinder housing.

Why is my flap not closing fully? This occurs when installation measurements are inaccurate. If the carcase bracket is set too far back inside the cabinet, the piston rod stroke will be insufficient to pull the flap flush against the carcase. Check your measurements and reposition the bracket by a few millimetres if necessary.