Sliding window rollers — sizing and replacing

A sliding window rides on rollers set into the bottom rail. When they wear, the sash drags, drops out of the interlock and starts to leak air. Sizing a replacement is straightforward if you take two measurements.

Measure the leaf weight and the track

Weigh a single sliding leaf — glass plus frame. A 2-track domestic window leaf is often 12–20 kg; a 3-track or a tall balcony leaf can be 30 kg or more. Then note the track profile: the wheel groove has to match the rail shape (flat, V or round) and the housing has to drop into the existing rail cut-out.

Single vs tandem

• Single-wheel carriages suit light leaves up to roughly 20 kg per pair.
• Tandem (twin-wheel) carriages spread a heavier leaf over four contact points and roll more smoothly. Use them on balcony sliders, 3-track systems and anything with laminated glass.

Pick a roller rated above the load per carriage — total the leaf weight and divide by the number of carriages, then choose one rated about 1.5× higher.

Adjustable height

Most quality carriages have a screw that lifts or drops the leaf a few millimetres. That is how you re-set the interlock engagement and the meeting-stile seal after fitting — not an optional extra.

While the sash is out

Replace the bottom guide, clean the track, and re-run the wool pile. New rollers on a gritty old track will wear again quickly.

Bring the old carriage or a photo with a scale, plus the leaf weight, and we will match a roller from stock.