Partial Extension Drawer Runners: Definition, Function & Differences from Full Extension

A partial extension runner is a drawer slide mechanism where the drawer can only be pulled out to approximately 70 to 80 per cent of its total length from the cabinet carcase. In contrast to a full extension runner, which provides complete access to the entire contents of the drawer, the rear quarter of the drawer remains inside the furniture piece with a partial extension fitting.

What exactly is a partial extension runner and how does it work?

From a technical perspective, a partial extension runner usually consists of a two-part rail system: the carcase profile, which is mounted to the inner cabinet wall, and the drawer profile, which is fixed to the drawer box. Because it lacks a third, intermediate profile, the runner cannot extend beyond its own installed length. This means that the rear section of the drawer stays inside the cabinet. However, this design makes the fitting very compact, robust, and less prone to faults due to the reduced mechanics. The steel material thickness for professional fittings is typically between 1.2 mm and 1.5 mm.

The difference compared to a full extension runner

The decisive difference lies in the extension travel. Whilst a partial extension stops at roughly 75 %, a full extension runner releases 100 % of the drawer box. Full extension drawer runners feature an additional intermediate profile (telescopic runner) that allows for total extension. Partial extension runners often offer higher lateral stability at the same material thickness, as fewer moving parts interlock with one another.

Types of partial extension runners

Depending on the design and the desired running action, various runner types are used:

• Roller runners: A classic system where plastic rollers glide within epoxy resin-coated steel channels. Frequently used as standard drawer roller runners in general furniture construction.
• Ball bearing runners: In this design, small steel ball bearings in a ball cage provide a precise, low-friction running motion.
• Undermount runners: The runners are fitted concealed beneath the drawer base. Corresponding undermount drawer runners offer a clean, sleek appearance when open.

In addition, these runners can be equipped with extra features. Damping (soft-close) ensures quiet, gentle closing, as found on soft-close drawer runners. This must not be confused with the tip-on feature (push-to-open). These are mechanically opposing mechanisms. A system for handleless fronts requires dedicated push to open drawer runners, where a spring-loaded pressure catch pushes the drawer outward rather than braking it upon closing. A mechanical compromise is the use of self-closing drawer runners, which simply draw the box closed mechanically over the final centimetres without hydraulic damping.

Dimensions, standards, and load capacity

The nominal length of the runner must be precisely matched to the internal depth of the carcase and the depth of the drawer. Standard lengths for partial extension runners range from 250 mm - 800 mm.

• For compact bedside tables or bathroom units, short variants such as 250 mm drawer runners or 300 mm drawer runners are suitable.
• In kitchen and office environments, 400 mm drawer runners and 500 mm drawer runners serve as the standard sizes.
• For deep sideboards or workshop cabinetry, lengths starting from 600 mm drawer runners are utilised.

The load capacity of a standard partial extension runner is usually between 20 kg and 30 kg. For tool chests or large pan drawers, this is often insufficient; in such cases, heavy duty drawer runners must be chosen instead, which can carry load capacities of 45 kg or more and are typically designed as full extension units due to their construction.

Application & selection

Partial extension runners are the workhorses among drawer slides – simple, durable, and mechanically reliable. They are ideally suited for desk pedestals, wardrobes, or basic chests of drawers where continuous access to the very back centimetre of the drawer is not strictly necessary. When planning the installation, bear in mind that the shorter extension travel can make inserting large organisers (such as wide cutlery trays) more difficult, which is why the clear opening width must be calculated in millimetres beforehand.