What are lock centres?
Lock centres are the vertical distance between the centre of the handle spindle hole and the centre of the keyhole or cylinder hole in a mortice lock. Together with the backset, it is the key dimension when you replace a lock or door furniture. In the Netherlands the same measurement is called steekmaat or PC distance (PC stands for profile cylinder).
Common sizes
- UK euro profile sashlocks: usually 47.5 mm centres (some makers quote 47 mm).
- uPVC multipoint locks: the gearbox often has 92 mm centres, but other sizes exist.
- Netherlands: 55 mm and 72 mm are the most common, with 85 mm and 92 mm as further standard sizes.
- Germany: room door locks to DIN 18251 commonly have 72 mm centres with a 55 mm backset.
Centres and backset
- Centres: measured vertically, spindle centre to cylinder or keyhole centre.
- Backset: measured horizontally, from the forend (the lock face at the door edge) to the spindle centre. Common UK sashlock backsets are about 44 to 45 mm or 57 mm.
Application
- Measure accurately. Remove the handle plate and measure from the middle of the square spindle hole to the middle of the round part of the cylinder hole. If in doubt, take the lock out: sizes are often stamped on the forend or case.
- Match a replacement lock. Same centres, same backset and same lock type, or the holes in the door will not line up.
- Order matching door furniture. Handles on a backplate have fixed holes for spindle and cylinder and must match the centres. Separate roses do not.
- Front doors. Use a security handle or escutcheon with cylinder protection, again matched to the centres.
Common mistake: ordering handles on a backplate from a photo or a rough guess. A few millimetres off and the cylinder will not fit through the plate.
Related terms
- Mortice latch
- Multipoint lock
- Rim lock
- Door handle
- Keyhole escutcheon
- Hardware (ironmongery)
Want to know more about building terms? Visit our knowledge base at fredsdiyplans.com.