How to Measure an Espagnolette for Replacement: Getting the Right Backset

How to Measure an Espagnolette for Replacement: Getting the Right Backset

Replacing an espagnolette requires accurate measurement, especially of the backset, if you want the new mechanism to operate correctly and align with existing keepers. This post explains how to measure an espagnolette for replacement with practical trade advice and clear DIY steps for UK homeowners and installers.

What is the backset and why it matters

The backset is the horizontal distance from the face of the locking stile or the front plate of the gearbox to the centre of the handle spindle or the centre of the locking follower. In simple terms: it tells you how far in from the profile face the mechanism’s operating centre sits. Getting this right is essential so that the handle and locking points line up with the keepers; an incorrect backset can leave the handle loose, prevent locking, or make the lock sit proud of the frame.

Tools and preparation

• Tape measure and steel rule;
• Vernier calipers or digital calipers for spindle diameter and finer measurements;
• Screwdrivers to remove handles and cover plates;
• Pencil and masking tape to mark measurements;
• Camera or phone to take reference pictures;
• Small spirit level or set square to check alignment.

Step-by-step: Measuring the backset

• Access the locking mechanism: Remove the handle roses/cover plates to expose the espagnolette gearbox spindle. Keep all screws carefully; take a photo so you remember reassembly orientation.
• Identify the face reference: For doors and windows, the face is the outer edge of the stile where the strike or keepers sit. Place the tape measure against that outer face to get a consistent reference plane.
• Measure to the spindle centre: Measure from the face to the centre of the spindle or the centre of the follower hole. Record this dimension in millimetres; this is your backset. If the spindle sits in a boss or plastic insert, measure to the centre of the boss.
• Check for any faceplate offset: Some espagnolette gearboxes have a faceplate that sits proud or recessed. If so, measure from the face of the frame to the front face of the gearbox, then add or subtract the offset to reach the spindle centre. Note both measurements.
• Confirm by remeasuring: Take the measurement twice and check with the original part if you still have it. If you are unsure, take photos and bring the old part when ordering.

Measuring additional critical dimensions

Backset alone is not always sufficient to select a replacement. Also measure and note the following:

• Spindle size and length: Measure the spindle profile (square or rounded) and width; common square spindles used in window furniture are often 7 mm or 8 mm. Measure the length projecting from the gearbox so the replacement handle will engage fully.
• Fixing hole centres: Measure vertical and horizontal distances between screw holes on the faceplate and around the gearbox. Many replacements use identical fixing centres; if not, you may need an adaptor plate.
• Overall gearbox depth and faceplate height: Useful if the frame is shallow or if a different depth would foul the rebate.
• Rod lengths and positions: For multi-point espagnolette rods, measure the lengths from the gearbox to the rod ends and note whether rods are fixed with clips or threaded ends. Also note rod diameter and profile.
• Keepers/strikers positions: Measure the position of keepers relative to the face so you can confirm that new keepers will align with locking cams or hooks.

Trade advice and common pitfalls

• Photograph everything before you dismantle: This saves time and prevents mistakes at reassembly. Include close-ups of the gearbox face and the keepers.
• Know handedness: Espagnolette rods and keepers can be handed. Note whether the handle operates clockwise or anti-clockwise to lock; mark left or right accordingly.
• Check spindle type: Some handles use a tapered or threaded spindle rather than a standard square; match this exactly. If unsure, measure the cross-section and thread pitch.
• Do not assume standard backsets: While some manufacturers stick to common dimensions, many older and bespoke frames use non-standard backsets. Measure rather than guess.
• Keep the old part: If it is possible, bring the old espagnolette to a specialist supplier; many trade counters will match by sight.

DIY fitting considerations

If you plan to replace the espagnolette yourself, these points will make the job smoother:

• Safety first: For doors, support the door if you detach the gearbox from the frame. For windows, rest the sash on a padded surface to avoid damage.
• Work methodically: Label screws and small parts with masking tape so you can replace them exactly as removed.
• Use correct fixings: Replace any corroded screws with stainless steel variations of the same length and thread for longevity.
• Adjust keepers if necessary: Many multipoint systems have adjustable keepers; fine adjustment can cure minor misalignment and prevent sticking.
• Test several cycles: Before finishing, operate the handle and locking several times to ensure smooth action and correct engagement at all points.

When to call a professional

If the espagnolette is integrated with the glazing or if rods are bent or seized, call a trade installer. Also contact a professional if the lock aligns poorly after replacement; a trained fitter can adjust keepers, rods and the strike plate to restore weatherproofing and security. If the frame is aluminium or a specialised profile, a supplier experienced with that manufacturer can supply the correct replacement parts.

Recommended Products

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

• ERAB Espagnolette Window Lock Universal Lock Replacement
• Avocet Slimline Offset Window Espag
• Multipoint Gearbox GU Old Style
• In-Line Window Mechanism
• Offset Window Mechanism

Conclusion and next steps

Correct measurement of the backset and associated dimensions is the key to a successful espagnolette replacement. Note the backset from face to spindle centre, measure spindle size and fixing centres, and confirm rod lengths and keeper positions. Take photos and bring the old part to a specialist if you can. For more on espagnolette systems and parts, see our pillar page: /guides/espagnolette-window-locks.

If you need help identifying a part, send measurements and photos to our trade counter or visit your local branch; we can advise on compatible gearboxes, spindles and keeper kits for a reliable replacement.