Spindle Sleeve Adapter

Frequently Asked Questions

How to use a spindle adapter

Most European door lever handles and mortise locks use an 8x8mm square spindle for the main door lever and a 6x6 mm square spindle for the privacy thumbturn — the industry standard across Europe. Bonaiti B-Smart mortise privacy lock, available in North America from Angelbau, is a typical example.

However, not every European-spec mortise lock body shares the same combination of square spindles. Multi-point and panic-function mortise locks, in particular, often use a larger 9x9mm or 10x10mm square drive. If a door lever manufacturer supplies their door levers with a standard 8mm spindle but your mortise lock requires a 9mm spindle, you need to add a spindle reducer to ensure the spindle fits snugly in the lock and operates reliably.

Spindle reducers (sometimes called transition sleeves, compensating sleeve, or step-down adapters) close the gap between square spindle dimensions, allowing you to pair different door levers and privacy thumbturns with third-party European mortise locks (i.e. Bonaiti, SSF, AGB).

Installing a spindle adapter does not require any special tools: slide the adapter over the spindle and step up to match the lock's follower opening — for example, 8/9mm or 8/10mm.

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