Scope: Uses Schlage residential bored-lock measurement instructions and the adjustable backset in the CISA Elettrika catalogue as examples. One brand's dimensions are not treated as standards for all locks.
Specifications
- Category
- Dimensions and compatibility
- English term
- Backset
- Reading focus
- Recording method
Finding the measurement datum
Schlage's help page defines backset as the straight-line distance from the door edge to the main face-bore centre. Measure to the centre, not the near or far edge of the hole.
Sources: [1]
Recording method
Mark the door edge and bore centre in a photograph before recording the value and unit. If a bore edge is damaged or the hole has been modified, state that the centre position is uncertain and have the installer verify it.
- Retain original units rather than recording a bare number.
- Draw the measurement line on the image to distinguish it from door thickness.
- Check the target model's drawing to confirm the same measurement location.
Why backset alone is insufficient
Matching backset establishes only one similar geometric condition. Replacing a lock also requires checking door thickness, bore diameter, faceplate, fixing holes and operating clearance. One dimension cannot establish complete compatibility.
Distinguishing fixed backset from an adjustable range
The CISA Elettrika catalogue lists adjustable backset of 50–80 mm for 11A721 and 11A731, a range supported by the same model. This differs from separately listed fixed-backset models in an ordering table. One value alone does not identify lock construction.
A range does not establish known adjustment increments. This catalogue page does not explain adjustment steps for every intermediate value. A range bar is not an installation instruction; check final position and strike alignment against the relevant instructions.
Also distinguish adjustable backset from adjustable latch projection: the former changes the relationship between the door-edge datum and operating centre, while the latter describes the bolt's own projection. Preserve the original parameter names in purchasing records rather than abbreviating both as adjustable.
Sources: [2]
Sources
- Schlage Residential · What is the Backset?
Backset definition and measurement datum; this brand's dimension range is not a universal standard.
- CISA · English catalogue: Elettrika, printed page 159 / PDF page 163
50–80 mm adjustable backset for 11A721/11A731; does not provide adjustment steps or mounting-hole positions.
Manufacturer documents are provided in their original language.