Flap Fittings & Gas Struts as Replacements for Hafele: Calculating Force Correctly

A gas strut or flap fitting holds furniture doors open using compressed gas; the required force is measured in Newtons (N) and depends precisely on the weight and height of the flap.

When an existing fitting on a wall cabinet – often installed by manufacturers like Hafele – loses pressure, the front drops down. For a replacement, it is not enough simply to select a visually similar component. The technical specifications must correspond exactly to the leverage of the cabinet flap. Like a shock absorber in a vehicle chassis, the gas strut must be precisely matched to the moving mass. If it is too weak, the flap closes by itself. If it is too strong, it jerks upwards when opened and can only be closed with substantial effort, which in the long run tears the hinges out of the carcase.

In this buying guide, you will learn how to calculate the correct extension force and determine the matching replacement fitting for installation.

Key Buying Criteria

When replacing defective lifting mechanisms on wall units, three technical parameters are decisive:

• Extension force in Newtons (N): This value indicates how much weight the strut can support during movement. Common gradations in furniture construction are 50 N, 60 N, 80 N, 100 N, 120 N, and 150 N. The value is usually printed on the cylinder of the old strut.
• Overall length and stroke: The total length in the extended state (centre of eyelet to centre of eyelet, e.g. 268 mm) must match the existing hole pattern. The stroke refers to the usable travel of the piston rod (e.g. 90 mm).
• Fixing system: Modern fittings often use System 32 for screwing the base plates into the carcase. The strut itself is usually clipped onto the mounting plate via a ball head.
• Opening angle: The fitting must harmonise with the concealed hinge used. For standard wall units, these are usually 90° or 110°.

Types and Options at a Glance

Depending on the construction of the furniture unit, different mechanisms are used.

• Gas struts for upward-opening flaps: The standard for upward-opening fronts. The compressed gas pushes the piston rod out and holds the flap open against gravity.
• Braking flap stays: These are used for downward-opening fronts (drop-down cocktail cabinets). They brake the fall of the flap and hold it horizontal. For this, you require special flap stays, as a regular gas strut would push in the wrong direction.
• Heavy-duty fittings: For very large or thick fronts made of MDF or solid wood, standard designs are insufficient. In these cases, components with a higher rated force and reinforced joints are used.

Which Strut for Which Case? Calculating Force Correctly

If the print on the old component is no longer legible, you must recalculate the required force. The rule of thumb is: 10 Newtons (N) corresponds to a holding force of approximately 1 kg.

However, because the flap is pivoted on hinges, leverage applies. The calculation requires the weight of the front including the handle, as well as the height of the flap.

Decision guide based on front weight (when using two struts per flap):

• Light fronts (up to 2.5 kg): If you are outfitting a small flap (e.g. 300 mm high, melamine-faced chipboard), choose struts with 50 N or 60 N.
• Medium-weight fronts (2.5 kg to 4 kg): For standard kitchen wall cabinets (e.g. 400 mm high, painted MDF), models with 80 N to 100 N are required.
• Heavy fronts (from 4 kg): If the flap is made of solid wood or is particularly tall, opt for 120 N or 150 N.

Note: From a flap width of 600 mm upwards, two struts (left and right) should always be installed in parallel to maintain torsional rigidity.

Installation Notes and Fitting

Replacing a defective fitting is usually possible without drilling new holes, provided the overall length is identical.

Required tools:

• Tape measure
• Screwdriver or cordless screwdriver with Pozidriv bit (PZ2)
• If necessary, a flat slotted screwdriver to release the clips

Steps:

1. Open the flap and prop it up securely.
2. Remove the old strut. Usually, the retaining spring on the ball head can be levered up with a small flat slotted screwdriver, allowing the strut to be pulled off.
3. Check that the mounting plates on the carcase and on the front are firmly seated. Tighten any loose screws.
4. Press the new strut onto the ball heads until it audibly clicks into place.
5. Important: Mount the strut so that the thick cylinder points upwards when the flap is closed. This ensures that the internal oil lubricates the seals and cushions the end stop.

FAQ – Frequently Asked Questions About Gas Struts and Flap Fittings

Can I replace a defective 80 N strut with a 120 N version? No. If the rated force is too high for the weight of the front, the flap can only be closed with substantial effort. Additionally, heavy pressure is exerted on the concealed hinge, which can cause the screws to tear out of the carcase.

Why is my cabinet flap no longer opening fully? This is the typical sign of pressure loss inside the cylinder. The gas gradually escapes over the years due to minimal wear on the seals. The component cannot be repaired and must be replaced completely.

Which hinge do I combine with a flap fitting? The strut only provides the holding function; the rotational movement takes place via the hinges at the top of the carcase roof. In most cases, standard concealed cup hinges with a 110° opening angle are used for this.

Are there struts with adjustable force? Pure gas struts have a fixed rated force set at the factory. However, there are mechanical flap stays where the friction resistance can be adjusted to the weight of the front using an Allen screw.

Matching Products and Categories for Your Project

To find the appropriate replacement for your unit, navigate directly to the respective components. Be sure to compare the Newton specifications and installation length before purchasing.

• Overview of all lifting and braking mechanisms: Flap Fittings
• Replacement parts for standard upward-opening wall units: Gas Struts
• Special versions for solid wood or extra-large fronts: Gas Struts for Heavy Flaps
• Braking stays for downward-opening bar compartments: Flap Stays
• Matching hinges for fixing the top of the flap to the carcase: Concealed Cup Hinges / Cabinet Hinges 110 Degrees