Full Extension, Single Extension & Over-Extension Runners: Definition & Comparison

May 3, 2026

A full-extension runner allows the drawer to be pulled out of the cabinet carcass by 100%, whereas a single-extension runner retains roughly 25% inside the cabinet due to its design. An over-extension runner extends beyond the nominal runner length, providing maximum access to the rearmost section of the drawer.

What Do the Extension Types Mean Exactly?

When building cabinet furniture, the extension type defines how far a drawer can be opened. This characteristic depends directly on the construction of the runner being used.

Single-extension (partial extension): The runner generally consists of two profiles. When opened, part of the drawer remains inside the carcass to ensure stability and prevent tipping. The extension loss is typically between 80 mm and 100 mm.
Full-extension: A three-part profile system is used here. Operating like a telescopic rod, the runner extends to its full installation length. The user enjoys unrestricted access to the entire contents of the drawer without the rear area remaining concealed.
Over-extension: This specialised design features an extended telescopic mechanism. The drawer does not merely pull out flush with the front edge of the carcass, but extends a further 30 mm to 50 mm beyond it, depending on the model.

Extension Types and Runner Systems

The type of extension is closely linked to the guiding system employed. The mechanical design determines running smoothness and load capacity.

Ball-bearing runner: Steel ball bearings inside a ball cage provide the movement. This system is very commonly used for full-extension drawer runners, as it can accommodate high loads and offers precise lateral stability.
Roller runner: Plastic rollers travel inside epoxy-coated steel profiles. This design is technically simpler and is traditionally used for single-extension setups. Matching models are found within the range of roller runner drawer runners.
Undermount runner: The runner is mounted concealed beneath the drawer base. It provides a hidden appearance and is manufactured in both single and full-extension variants. Further details can be found in the category for undermount drawer runners.

Dimensions, Load Capacity, and Technical Standards

During planning, the installation length (nominal length of the runner) and the depth of the cabinet carcass must correspond. Length increments in the furniture industry usually progress in steps of 50 mm. Common sizes for standard carcasses include 400 mm drawer runners, 500 mm drawer runners, as well as 600 mm drawer runners.

The load capacity indicates the total weight (drawer including contents) that a pair of runners can dynamically support in the extended state. Standard runners generally carry 25 kg to 30 kg. For workshop trolleys or deep pan drawers in kitchens, heavy-duty drawer runners are an absolute necessity, as these are designed for loads of 45 kg, 80 kg, or even over 100 kg.

Additional Functions: Soft-Close and Opening Mechanisms

Modern runner systems are frequently equipped with additional mechanical features that increase user convenience. A strict distinction must be made between two contrasting mechanisms:

Soft-close: An integrated hydraulic damping system absorbs the momentum of the drawer when closing, gently and silently pulling it shut over the final few centimetres. This is frequently achieved using soft-close drawer runners.
Push-to-open: An ejection mechanism for handleless fronts. Light pressure applied to the closed drawer front tensions a spring that subsequently pushes the drawer open by a short distance. By design, such push-to-open drawer runners cannot be combined with standard soft-close damping, as the trigger point requires a firm stop.

Application & Selection: Which Extension for Which Project?

The choice of extension type depends on the carcass depth and intended application. A single-extension runner is entirely sufficient for shallow desk drawers or small bedside tables. However, as soon as the carcass depth exceeds 400 mm, full extension becomes the technical standard in order to eliminate blind spots at the back of the drawer. Over-extension runners are primarily fitted in suspension file cabinets or specialised machinery furniture where components must be lifted out from above using a hoist.