Mortise Lock Case Comparison 2026: Every Published Backset and Centre Distance, Side by Side

Every mortise lock case is described by two numbers before anything else: the backset, from the face of the door edge to the centre of the spindle, and the centre distance, from the spindle to the centre of the cylinder. Get those two right and the handle and the key line up with the holes in the door. Get either wrong and nothing else about the lock matters, because the holes are already drilled.

This guide lays out every lock case in our catalogue that publishes both numbers (27 of the 58 lock-case records, as of September 2026) side by side, so a buyer can find the case that fits a door rather than reading 58 product pages. The tables are generated from the specification rows on those pages; nothing in them is estimated.

HOW TO READ THE TABLES

Both measurements are published in millimetres, with the inch equivalent alongside. Backset is measured from the outer face of the faceplate, not from the case behind it. The difference is the faceplate thickness, and it is enough to put a lever off-centre on its rose. Centre distance is measured between the centre of the square spindle hole and the centre of the cylinder hole. Where a record also publishes a cylinder type, a bolt arrangement or a faceplate size, it appears in the last column; "not published" means the record does not state it, not that the feature is absent.

TWO FAMILIES: NARROW STILE AND STANDARD

The first thing the numbers show is that our lock cases fall into two families that do not overlap. Backsets of 20 to 35mm are narrow-stile cases, made for aluminium framed doors whose vertical stile is too narrow to take a conventional lock, and 9 of the 27 are in this group. Backsets of 40mm and above are standard cases for timber and steel doors, and 18 are in that group. Our article on why aluminium doors drop explains why a narrow-stile door needs its own kind of lock case and cannot simply take a short-backset version of a standard one.

Narrow-stile cases, by backset:

Standard cases, by backset:

THE CENTRE DISTANCE DECIDES THE HANDLE

Across the published cases, 85mm (3-3/8") is by far the most common centre distance: 18 of the 27, including eight of the nine narrow-stile cases. The others are 72mm (three cases: LC32, LC33-5572 and LC34), 68mm (LC6860), 65mm (the three LC7065 variants), 92mm (LC9230) and 45mm (LC9045).

That matters because the centre distance is shared with the handle. A lever on a long plate, and any trim that carries the cylinder hole on the same backing, is drilled for one centre distance, and it only works with a lock case of that same distance. On a new door, pick the centre distance first and the handle second. On a replacement, the existing holes have already picked it for you: measure them, and look for that number in the tables before anything else. Our articles on the stainless 9000 levers and on the LH lever range explain how a plate's hole spacing is matched to the case.

Different markets standardise on different centre distances, and a supplier who serves several markets will stock several. That is the reason a range like this one carries 85mm alongside 72mm and 92mm: each is the right answer for somebody's doors.

WHAT A SHORT BACKSET COSTS

A narrow-stile case solves one problem and creates another. With a 20 or 25mm backset the spindle sits very close to the door edge, and so does the handle, which means the gap between the handle and the frame, or the adjacent leaf on a pair, is small. A lever with a long return or a knob can trap knuckles against the frame every time the door is opened. That is why narrow-stile doors are usually fitted with narrow-stile levers, pull handles or push pads rather than the handles that suit a timber door, and why the backset should be chosen together with the handle, not before it. If the stile allows 30 or 35mm, the extra space is worth having for the hand alone.

SUFFIXES ON THE MODEL NUMBERS

Several cases carry letters after the numbers: B on the LC8520B, LC8525B and LC8535B, BK on the LC8530BK, PS on the LC8520PS, LC8530PS and LC7065PS. On our cylindrical locks, PS means passage and BK means privacy, and it is tempting to read these the same way. The lock-case records do not define their suffixes, so we will not decode them here. Where the difference between two variants matters (a latch-only case against a deadlocking one, for example), say which function you need in words, and we will match it to the variant rather than the other way round.

MODEL NAMES DO NOT FOLLOW ONE ORDER

Most of these model names contain the two numbers, and it is tempting to read the lock straight off the name. Do not. The naming is not consistent across the range. LC8530 and LC6860 put the centre distance first and the backset second; LC32 65×72mm and LC34 50×72mm put the backset first. The LC7065 variants and LC9045 read correctly only in backset-first order: their records say backset 70mm with a 65mm centre, and backset 90mm with a 45mm centre. Those two are the outliers in the tables, and if either is the case you want, confirm both numbers with us before ordering.

The rule that follows is short: read the specification rows, never the name. The tables above are built from the rows for exactly that reason.

WHAT THE TABLES LEAVE OUT

Two kinds of gap are worth knowing. First, 31 lock-case records do not publish both numbers and are not in the tables. Some publish only a backset (LC17 at 16mm, LC5845 at 45mm), some only a faceplate, and some nothing yet. Second, most of the cases that are in the tables publish only the two numbers and not the rest of the geometry. Only the LC07 publishes its full set: a 240 × 23mm faceplate, a 173mm case height, 72mm case depth, a 26mm latch throw and an 18.5mm bolt projection.

That second gap matters when you are replacing a lock in an existing door, because faceplate length and case depth decide whether the new case fits the old pocket. Our article on cross-referencing a lock you already buy sets out the six numbers that decide interchangeability; if the case you want publishes only two of them, ask for the other four before ordering, and we will measure them rather than estimate them.

CHOOSING, IN THREE STEPS

First, the door decides the family: an aluminium narrow-stile door takes a case from the first table, a timber or steel door from the second. Second, the backset is set by the door preparation or by where the handle should sit on the leaf, and on a replacement by the old lock. Third, the centre distance is set by the handle or trim you intend to use, or by the holes already in the door. Only after those three does the function (latch only, latch and deadbolt, passage) narrow it to one model, and only then does finish enter the conversation.

Send those three facts with an enquiry and the reply can name a case from these tables the first time. Send a model name alone and, as the naming section shows, it may name the wrong one.