Full Extension vs Partial Extension vs Over Extension: Which Drawer Runner to Choose?

A full extension runner extends by 100%, a partial extension runner reveals around 75% of the drawer depth, and an over extension runner travels beyond the front edge of the carcass.

When planning carcasses and drawer systems, choosing the right runner guide is crucial for subsequent ergonomics and load capacity. The extension distance defines how far a drawer can be pulled out of the piece of furniture before reaching the mechanical stop. This guide breaks down the technical differences between the three main types and offers a basis for decision-making in furniture construction.

What is a Partial Extension Runner?

A partial extension runner does not allow the drawer to be pulled fully out of the cabinet. As a rule, around 20% to 25% of the drawer depth remains inside the carcass.

Technically speaking, this runner usually consists of two profiles. Often, a simple roller drawer runner is used here, in which plastic rollers run inside powder-coated metal tracks. With this design, the rear section of the drawer is harder to see and reach. The mechanism is straightforward, low-maintenance, and requires little lateral installation space.

What is a Full Extension Runner?

A full extension drawer runner reveals the entire interior of the drawer. When fully opened, the back panel of the drawer sits flush with the front edge of the carcass.

Mechanically, this functions like a multi-part telescopic aerial: the runner consists of at least three interlocking profiles. This is frequently implemented as a ball bearing runner, where steel ball bearings in a ball cage ensure a precise and tilt-resistant movement. Especially with deeper carcasses that require 500 mm drawer runners or 600 mm drawer runners, for example, full access to the rear storage space provides a massive ergonomic advantage.

What is an Over Extension Runner?

An over extension runner goes one step further. Here, the drawer can be pulled out of the carcass beyond its own length. The extension distance is therefore more than 100% of the nominal length (frequently 30 mm to 50 mm extra).

This special design is achieved via extended intermediate profiles in the telescopic runner. Over extension is primarily used where overhangs such as worktops, thick counter edges, or other structural obstacles would obstruct access to the open drawer from above.

The Differences in Detail

To determine the correct runner for a specific piece of furniture, the specifications of the extension types must be compared:

• Access and ergonomics: Partial extension conceals the rear quarter of the drawer. Full extension provides unrestricted access from above. Over extension moves the drawer completely forward of any potential furniture overhang.
• Load capacity: Partial extension runners are usually designed for lighter loads (up to approx. 25 kg). Full extension and over extension runners often provide higher load ratings due to their multi-part construction. For workshop trolleys or deep pan drawers, a heavy-duty runner is required, capable of supporting weights from 45 kg to over 100 kg. Suitable models can be found among heavy duty drawer runners.
• Complexity and installation dimensions: A partial extension runner is more forgiving during installation, as the tolerances on roller runners are slightly more generous. A full extension runner with ball bearings requires precise fitting, often with an exact lateral installation clearance of 12.7 mm to 13.0 mm per side.
• Additional functions: High-grade runners can be fitted with convenience features. Important for planning: soft-close and push-to-open are contrasting mechanisms. Soft-close drawer runners brake the drawer upon closing and pull it gently shut. Push-to-open drawer runners (tip-on) push the handleless drawer outwards via pressure on the front panel.

Which Extension Runner Should You Choose for Each Case?

The choice of runner depends on intended use, drawer depth, and budget.

When is a partial extension runner sufficient? For short drawers in standard chests of drawers, bedside tables, or desk pedestals, a partial extension is often sufficient. If you are fitting 250 mm drawer runners, for example, the concealed area is so minimal that the contents remain easy to reach.

When is a full extension runner essential? In kitchens (pan drawers, cutlery trays), in workshops, and for deep office cabinets, full extension is the standard. As soon as you plan nominal lengths from 400 mm drawer runners upwards, a partial extension becomes impractical because the blind spot at the back becomes too large.

When do you need an over extension runner? You should only select this runner under specific geometric conditions. When a piece of furniture has a wide overhanging top panel, or when you need top access to the rearmost connections of a rack unit in a server cabinet, the over extension runner demonstrates its strengths.

Frequently Asked Questions (FAQ)

Can I replace a partial extension runner with a full extension runner?

Yes, this is generally possible provided the lateral installation dimension (the clearance between the drawer side and the internal carcass wall) is identical. For standard ball bearing runners, this measurement is usually just under 13 mm. In addition, the nominal length of the runner must match the depth of the drawer.

Are full extension runners available for concealed installation?

Yes. If the runner hardware should not be visible on the sides of the drawer, an undermount runner is used. This is fitted beneath the drawer base. Corresponding systems can be found among undermount drawer runners.

Why does my full extension runner jam over the last few centimetres?

If a full extension runner does not close completely or feels stiff, an installation error is often the cause. The runners must be fitted exactly parallel and at right angles to the front. A deviation of just 1.5 mm between the carcass width at the back compared to the front can cause the ball cage of the telescopic runner to jam.