Window Handle Spindle Sizes Explained: 7mm and 8mm

Choosing the correct window handle spindle size is a small decision that makes a big difference during installation, replacement or servicing. Tradespeople and DIY enthusiasts often encounter two common spindle sizes: 7mm and 8mm. This guide explains what those numbers mean, how to measure spindles, and practical tips for fitting and troubleshooting. If you need a replacement window handle, this article will help you get the right fit first time.

What the spindle size means

The spindle is the square rod that passes through the window mechanism and connects the window handle to the gearbox or locking mechanism. When we say a 7mm or 8mm spindle, we refer to the width across the flat faces of the square spindle. Choosing between a 7mm and 8mm spindle is crucial because:

• A correctly sized spindle ensures the handle engages the mechanism without play; an incorrect size will cause slop or fail to turn the gearbox.
• Mainstream manufacturers use 7mm and 8mm as standard sizes for many casement and tilt-and-turn windows.
• An accurate spindle size makes retrofitting new window handle hardware quicker on site.

How to measure a spindle: step-by-step

Measuring a spindle is straightforward and prevents wasted visits or returns. Use a caliper or a precise ruler and follow these steps:

1. 1Remove the existing handle by undoing the grub screw or cover plate screws; keep fixings safe.
2. 2Pull the handle off the spindle to expose the square section fully.
3. 3Measure the width across the flats of the square spindle to the nearest 0.5mm. Round down if between sizes.
4. 4Measure the spindle length from the base of the handle seat to the end of the spindle; note any captive sleeves or collars.
5. 5Check if the spindle is handed or centred: some windows need an off-centre spindle to reach the gearbox square tub.

7mm vs 8mm: differences and common uses

Both 7mm and 8mm spindles are common in the UK; the choice usually depends on the window make and age. Practical differences include:

• 7mm spindles: commonly found on older or budget PVCu handles; easier to find in heritage or slim-profile fittings; slightly less torque transfer than 8mm.
• 8mm spindles: more common on modern PVCu and aluminium windows; provide a firmer engagement and are preferred for heavy-duty locking mechanisms.
• Adaptor options: where the mechanism requires a different size, adapters and replacement spindles are available; however, direct fit is always the best long-term solution.

Choosing the right replacement: practical checklist

Before ordering a replacement window handle, use this checklist to guarantee compatibility:

• Confirm spindle width: 7mm or 8mm measured across flats.
• Confirm spindle length: measure from handle seat to spindle tip in millimetres.
• Check centre distance if applicable: the distance between screw fixing centres on the handle rose or backplate.
• Decide on handedness: some handles need a left or right orientation; reversible handles are available for flexibility.
• Consider locking options: if the window handle must be lockable, check key or push-button options and whether the spindle and gearbox accommodate a locking function.
• Material and finish: choose corrosion-resistant finishes for coastal installations; ensure aesthetic match with existing hardware.

Installation tips for tradespeople and DIYers

Fitting a new window handle is usually a quick job if you prepare properly. Follow these tips for a professional finish:

• Always isolate the window mechanism before working: rest the window on stay pins or support to prevent movement.
• Use a torque-limited screwdriver for fixings to avoid stripping the rose or backplate screws on aluminium frames.
• If the handle feels loose, check the grub screw against the flats of the spindle; replace worn grub screws rather than over-tighten.
• When replacing an 8mm spindle with a new handle, ensure the grub screw depth is sufficient; some aftermarket handles come with longer grub screws to reach deeper spindles.
• Test operation through the full travel several times; the locking points should engage smoothly without binding.

Troubleshooting common problems

Even experienced installers run into issues. Here are common problems and quick fixes:

• Handle spins without operating locking points: likely worn spindle flats or wrong size; measure and fit a correct 7mm or 8mm spindle.
• Handle stiff to operate: check gearbox lubrication and alignment; ensure the spindle is straight and not bent.
• Squeaking or rough movement: remove handle, clean spindle and apply a small amount of light machine oil to the interface.
• New handle fouls the frame: verify spindle length and backplate profile; trim or fit a shorter spindle if necessary, or use a slim-line backplate.

Understanding spindle sizes, especially the common 7mm and 8mm squares, saves time and reduces call-backs. Whether replacing a single window handle in a domestic property or fitting dozens on a new build, measuring accurately and choosing the right spec makes the job straightforward.

Conclusion: The two sizes you will most often encounter are 7mm and 8mm. Measure across the flats, check spindle length and handedness, and select the handle with the correct fixings and finish. With the right preparation and tools, replacing a window handle is a simple task for any competent tradesperson or confident DIYer. For more detailed guides on handle styles and fitting techniques, visit our guides section: /guides/window-handles.

Recommended Products

Based on this article, you may find these products helpful:

• TSS Cockspur Window Handles
• TSS Offset UPVC Window Handles
• ERA Universal Inline Window Handle
• In-Line Window Handle - White
• In-Line Window Mechanism