Bored lever or knob set (ANSI/BHMA A156.2)
Two bores: a 2-1/8 in cross bore through the face for the knob, and an edge bore for the latch. Dimensions are so consistent that a retrofit can be designed blind — backset 2-3/8 in or 2-3/4 in covers almost everything.
Also called: Tubular lockset · Bored lock · Entry lever · Knob set
Anatomy
- Chassis inside the cross bore
- Latch assembly in the edge bore, with a 2-1/4 × 1-1/8 in faceplate on residential sets
- Tailpiece connecting the outside trim to the chassis
- Cylinder in the outside knob or lever, or a separate deadbolt above
Parameters to measure
Measure in this order: Backset (Dornmaß) → Cross bore diameter → Edge bore diameter → Door thickness
| Parameter | Typical values | Tolerance that still fits | How to measure |
|---|---|---|---|
| Backset (Dornmaß) | 2-3/8 in (60 mm) residential, 2-3/4 in (70 mm) exterior and commercial | Adjustable latches cover both | Door edge to the centre of the 2-1/8 in bore. |
| Cross bore diameter | 2-1/8 in (54 mm) | — | Measure across the round hole in the door face. |
| Edge bore diameter | 1 in (25 mm) or 2-1/8 in | — | Measure the hole in the door edge. |
| Door thickness | 1-3/8 to 1-3/4 in (35–45 mm) | Thicker doors need extension kits | Measure at the bore. |
Retrofit architectures that work
- Motor replacing the interior handle — The interior lever or knob is replaced by a motor unit that drives the 8 mm spindle directly. The outside keeps the original key cylinder and handle. This is the cleanest fit for mortise locks where the bolt is thrown by the key and the handle only retracts the latch.
- Full lock replacement on the same footprint — The old lock case is removed and a smart lock with the same footprint takes its place. This is the dominant approach in East and Southeast Asia, where push-pull digital locks replace mortise sets on HDB, condo and apartment doors.
- Surface motor on a deadbolt turn-piece — An adhesive or screw-fixed motor sits on the door face and rotates the existing deadbolt turn-piece. Nothing is drilled. This is the standard approach for North American single-cylinder deadbolts and for many Asian rim deadbolts.
Two very different retrofits live here. On a lockset with a key in the knob, you replace the whole set with a smart lockset on the same bores. Where there is a separate deadbolt above, the cheap and reliable answer is a motor on the deadbolt's turn-piece instead.
Related standards
ANSI/BHMA A156.2 · ANSI/BHMA A156.36
Questions
What does Grade 1 mean?
The highest ANSI/BHMA durability grade. For bored locksets Allegion lists 1,000,000 cycles at Grade 1; other published tables give 800,000. Cite the edition when you use the number.
Can I just swap the outside knob?
Usually no — chassis and tailpiece geometry differ between makers even when the bores match.