Guide
Types of Door Locks in the UK: What Each One Is and Where It Fits
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At a Glance: Every UK Door Lock Type
Why Lock Names Get Mixed Up
Some locks take their name from the complete mechanism; others are named after the part that accepts the key. As a result, the terms mortice lock, nightlatch, euro cylinder and multipoint lock are regularly mistaken for one another, despite referring to different components or systems. This guide sorts them out: it covers the common door lock types in UK homes, how to recognise each and what its main parts do, and it shows where useful markings sit while explaining why appearance alone cannot confirm a lock's exact model or security standard.
The Matrix
| Name | Typically fitted to | Identifying feature | Distinction |
|---|---|---|---|
| Euro cylinder with a single-point lock | Some timber, aluminium and metal doors | Euro-profile keyway, with no long strip and no row of locking points | One central lock case, operated by the cylinder |
| Surface-mounted rim lock | Some older timber doors, internal doors and outbuildings | Complete case visible on the inside face | Mounted on the surface, not recessed into the door edge |
| Nightlatch with rim cylinder | Mainly timber entrance doors | Box-shaped case on the inside face, separate cylinder visible outside | Usually latches when the door is closed |
| Mortice deadlock | Mainly timber entrance doors | Case recessed into the edge, bolt visible when the door is open | Key-operated bolt, no handle-operated latch in the same case |
| Mortice sashlock | Timber entrance doors and internal doors | Case recessed into the edge, spring latch and locking bolt both visible | Handle-operated latch combined with a separate lock |
| Euro cylinder with a multipoint lock | Common on uPVC and composite doors | Euro-profile cylinder near the handle, long locking strip along the edge | The cylinder accepts the key and the wider mechanism controls several locking points |
If a lock needs repairing or replacing, you may be asked early on which type you have, and the keyhole will rarely give the complete answer. The most dependable starting point is the door: what it is made from, where the mechanism sits, and what is on the inside face and along the edge. Using these clues can make it easier to tell a mortice lock, a nightlatch, a rim cylinder and a multipoint system apart. Keep in mind that each row describes a lock family and not an exact model. Multipoints can be found on modern timber doors; aluminium and metal doors may be fitted with cylinder-operated lock cases. The choice of any replacement part requires product markings and measurements beforehand. The middle pair of columns is where most readers trip up, so the next sections look at each of them.
Timber Doors and the Locks Fitted Into Them
A timber door tends to hold a lock within its edge, a latch on its inside face, or both: a keyhole in the edge of the door means a mortice lock, and a key that goes through the face to a box on the inside means a nightlatch. The common options on timber are mortice locks, nightlatches, surface-mounted rim locks or two separate systems, and the giveaway is whether the case is inside the edge or visible on the inside face.
Nightlatches and Their Rim Cylinders
A nightlatch is fixed to the inside face, operated from outside by a rim cylinder, and usually latches when the door is shut. Although a traditional rim lock is also attached to a timber door's inner face, it is not always a nightlatch. The case may contain a latch, a bolt or both, it may not latch automatically like a typical nightlatch, and the mechanism may be operated by a key, handle or knob.
Mortice Sashlocks and Deadlocks
A deadlock has a bolt worked by a key and no latch. A sashlock combines a latch operated by handles with a separate bolt.
Where a timber entrance door has both a nightlatch and a separate mortice lock, they operate independently, do different jobs and should be identified separately. A multipoint lock is a complete locking system of connected parts, commonly fitted to uPVC and composite doors, although some timber and aluminium doors use one too; operating it moves locking points along the door edge into keeps fitted to the frame.
How to Read the Name of a Lock
Once you know the order, a product name stops being jargon. It usually runs maker, lever count, where the lock fits, what it does, and then any finish, case size or standard. So [Maker] five-lever mortice sashlock decodes as a named manufacturer, five internal levers, a case fitted inside the door, and a combined latch and deadbolt. Each element describes a different aspect, so recognising one term does not confirm the full specification, and that five-lever description on its own does not mean the lock meets BS 3621.
What Each Term Means
- Mortice: the case is recessed into the door edge
- Rim: the main body is mounted on the door surface
- Deadlock: a bolt but no spring-operated latch
- Sashlock: a deadbolt combined with a handle-operated latch
- Nightlatch: surface-mounted, normally latching as the door closes
- Cylinder: the key-operated component that activates the mechanism
- Multipoint: a connected mechanism with locking points along the edge
- Case size, backset, finish: the case's overall depth; the distance from faceplate edge to keyhole, cylinder or spindle centre; the visible surface, such as brass, chrome or satin nickel
These narrow the family and dimensions but do not confirm a fit, because keyhole, spindle, faceplate and fixing points may sit differently.
Lever Counts: What They Actually Mean
Before a lever mortice lock's bolt can move, the key must lift its levers to set heights: three in a three-lever lock, five in a five-lever. Three-lever locks often appear on internal doors; five-lever locks are common on external timber doors. Equal counts can hide different materials, construction, bolt design and tested performance, so the count is not a security verdict or a test of what an insurer requires.
The Markings on the Faceplate
Marks are easiest to find on parts visible while the door is open. Mortice and multipoint faceplates may show a maker's name, logo, series or code. Even with a code visible, confirm the lock type and measurements before ordering, because similar components appear across ranges. Do not dismantle a lock case, gearbox or strip to search for a hidden number.
Multipoint Locks Are Not All One Type
A full-height locking strip sits along the edge of a uPVC or composite door, and its make cannot simply be exchanged for another. That strip is the multipoint assembly the handle operates. The euro cylinder is a separate component turned by the key. Someone asking about a uPVC door's lock type usually needs the identity and arrangement of the strip, rather than the cylinder alone.
The Strip Itself and What It Tells You
Start with the door safely open and inspect the visible faceplate. A multipoint links several securing positions to a central gearbox. Hooks, rollers, pins and bolts can appear in different combinations, with corresponding keeps fitted to the frame. This family is common on composite and uPVC doors and occurs on some timber and aluminium examples as well.
| Visible or connected part | What to understand |
|---|---|
| Central mechanism | The gearbox coordinates movement received from the handle and cylinder |
| Handle spindle | Connects the handles through the door and transfers their action to the gearbox |
| Cylinder | The keyed unit that activates the surrounding lock |
| Edge strip and faceplate | Connect the gearbox with locking components farther along the door |
| Projecting locking parts | Hooks, bolts, pins or rollers that locate into frame keeps |
| Keeps on the frame | Accept the latch and the relevant locking points |
Identification involves more than counting projections. Capture the manufacturer name or symbol, stamped references and any label near the latch. Note where the gearbox lies, which locking-point shapes are present and how they are spaced. Include clear photographs of the complete edge, handles, cylinder and markings when seeking help with identification.
PZ describes the separation of the handle spindle centre from the cylinder centre. Backset describes the cylinder centre's depth relative to the faceplate edge. Although useful clues, these dimensions can match on mechanisms with incompatible gearbox connections, faceplates or point positions. Replacement ordering needs accurate measurements, addressed in the separate guide covering cylinder changes.
The action also varies. Raising a handle often extends the locking parts, with a subsequent key turn preventing their release through the handle. Some strips instead engage on closure, while others use key movement to drive their locking points. Observing that action will not establish the manufacturer or exact model.
Treat symptoms as clues rather than a diagnosis. A key refusing to rotate can indicate cylinder trouble. Handle travel without movement at the strip can involve the spindle or gearbox. A lock that behaves normally while open but resists when closed may have a door or keep alignment problem. Stop forcing stiff components: wear, misalignment and internal faults can all create resistance, and additional force can increase damage. A fault in one part need not require replacement of the whole assembly.
Understand What Each Specification Proves
Descriptions often mix installation type, mechanism, lever number, dimensions, appearance and tested security. Recognising a single term cannot establish the entire specification.
| Term | Meaning in a description |
|---|---|
| Rim | The main body sits on the door's surface |
| Mortice | The case fits into a recess cut into the edge |
| Sashlock | A handle-operated latch shares its case with a deadbolt |
| Deadlock | A bolt mechanism without a spring-operated latch |
| Nightlatch | A surface-mounted unit that usually latches as the door closes |
| Case size | Mortice case depth, often stated in millimetres or inches |
| Backset | Faceplate-edge distance to the centre of the keyhole, spindle or cylinder |
| Finish | The external colour or treatment, such as chrome, brass or satin nickel |
Those terms describe families and dimensions, but a replacement can still differ at its spindle, keyhole, faceplate or fixing locations.
A cylinder recognises the inserted key and passes its rotation into the surrounding mechanism. That mechanism might be a mortice case, surface nightlatch or multipoint gearbox. Replacing the cylinder changes key access and can improve protection against some attacks, but it leaves gearbox wear, damaged strips, loose handles and alignment faults unresolved. If the complaint persists, the lock case, spindle, frame keeps and associated mechanism still need assessment.
Euro profiles are narrow with a rounded upper portion. They commonly serve composite, aluminium and uPVC doors, and occasionally timber ones. A cylinder with a single keyed face is a single cylinder; keys operating both faces identify a double version. A thumbturn uses an outside key and an inside turning knob. Usually an edge screw retains the cylinder as it passes through the door and gearbox. Choose length to suit the thickness occupied by the door and handles. An overly exposed outer end may be easier to attack physically.
An oval cylinder has a rounded oval shape and carries out a comparable job. It appears less frequently in new domestic installations but remains in existing doors and older mechanisms. Neither similar overall length nor similar function makes it interchangeable with a euro cylinder. The furniture opening and lock case must be intended for its profile. Establish the shape, complete length, fixing position and key or thumbturn arrangement on both faces. Problems involving stiffness, uncertain locking or handle movement also require checks beyond the cylinder. For a security upgrade, compare tested standards and resistance to picking, drilling, snapping and other attacks, since product features vary considerably.
Lever counts describe internal workings. The key must position a lever lock's internal levers at particular heights before its bolt can travel. Three-lever and five-lever labels state how many are present. A five-lever mortice sashlock therefore has a recessed case containing five levers, a latch and a deadbolt. Three-lever models often suit internal applications, while five-lever models are common on timber entrance doors. Materials, construction, bolt details and tested performance can differ even with identical counts. Entrance suitability and insurance requirements need more than that number.
A five-lever designation does not mean the lock satisfies BS 3621. Under BS 3621, mechanically operated single-point assemblies are assessed for thief resistance, with keys required to lock and unlock on each face. The assembly's tested performance determines compliance. The edition currently in force is BS 3621:2017+A1:2024. A reference normally appears on a compliant lock or its packaging, often accompanied by a certification mark. Read it in full because older hardware may cite an earlier edition, and verify the exact product model. Neither bolt length nor a recognisable brand substitutes for that evidence. Keyless opening from the inside may fall under a different standard, as BS 3621 specifically addresses exit by key.
Which Door Each Type Belongs On
Door First, Lock Second
Every type in this guide is explained by one rule: the door decides the lock. Read the door and the lock usually follows.
| Door | What it normally carries |
|---|---|
| Timber, external | A mortice lock, often with a nightlatch |
| uPVC or composite | A euro cylinder in a multipoint strip |
| Aluminium or metal | A multipoint or a cylinder-operated lock case |
| Timber, internal | A lighter mortice latch or sashlock |
| Older timber door or outbuilding | Sometimes a surface-mounted rim lock |
Two exceptions break the pattern. Newer timber doors can be built with multipoints, so age often tells you more than material. A flat entrance door onto a shared corridor has its own considerations, since the method of exit is part of what suits it and a lock opening from inside without a key may come under a different standard.
What to Settle Before a Replacement
Identification narrows the problem but does not confirm the faulty part or its replacement, because similar-looking locks differ in size, operation, security specification and compatibility. Ask four questions: what is fitted; what is causing the fault, given that a stiff key or loose handle may come from the cylinder, case, gearbox, spindle or alignment; whether one part or an adjustment would do; and whether the replacement will fit, work reliably and secure that entrance. Broad labels such as "euro cylinder" or "five-lever sashlock" cannot pin down a part. Brand names and anti-snap labels prove no standard, which belongs to a specific product. If lock changes follow lost keys, a move or a break-in, key control and damage matter as well as fit. When in doubt, arrange an inspection before buying; a clear diagnosis can prevent an unnecessary full lock change.
Types You Are Less Likely to Meet
Some door locks are simply less common, and they usually work alongside a main lock instead of doing its job.
- A door bolt is surface-mounted and moved by hand, giving the door a second fixing point.
- A hinge bolt helps the hinge edge resist being forced.
- A push-button lock is a mechanical digital lock released by a code, with no batteries, wiring or app. Offices, storage rooms, shared areas and some residential side entrances use them. There is a numbered keypad outside and a knob, lever or thumbturn inside, and the correct code frees the handle to drive the latch or case, possibly a separate tubular latch, mortice latch or lock case. The keypad mechanism, spindle, latch, internal case or alignment may explain why entering the correct code has stopped releasing the door.
- A sliding patio door lock sits in the handle assembly or is connected to a mechanism in the vertical edge of the panel. It may use a single hook or bolt, multiple hooks or locking points, a key cylinder, a separate handle and thumbturn, an anti-lift device and keeps on the meeting frame or fixed panel. The handle shape, fixing positions, cylinder profile and edge faceplate are the clues to look at.
- A window lock belongs to its own family, with its own fittings.
Smart locks and other electronic locks, access control and master key suites are left out of this guide, and they are not something we work on. For a quick view of the main types, return to the comparison table above.
Not Sure What Lock You Have? Ask Us
If you have reached the end of this guide and the lock is still a mystery, ask. We will tell you what it is, what repairing or replacing it would take, and the price, before anything is touched.
Have to hand: the door material, where on the door the keyhole sits, and a photo of the faceplate along the open edge. If the entrance cannot be secured at the moment, mention that first.
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Door Lock Type Questions
How can I tell what type of door lock I have?
First establish the door's material, then decide whether the lock occupies a recess in its edge or rests on its surface. For identification, consider the keyhole and faceplate alongside any handles and the number of locking positions. Those clues distinguish a cylinder or multipoint mechanism from a nightlatch or mortice lock. A key moves a deadlock's bolt, with no handle latch. Sashlocks pair a spring latch with a deadbolt, normally needing handles and a keyhole.
What type of lock is usually fitted to a uPVC door?
Most modern uPVC front doors have multipoint locking, controlled through the handles and a euro cylinder. Look beyond the cylinder when identifying the system: the full arrangement also takes in a gearbox, hooks, the locking strip and keeps fitted to the frame.
How do I know if I have a mortice lock or a nightlatch?
Identify a nightlatch by its visible body on the door's inner surface, or a mortice lock by its recessed position in the edge. These are not mutually exclusive fittings. On a timber entrance door, the presence of either type leaves open the possibility of the other.
Is a euro cylinder the same as a multipoint lock?
A multipoint lock includes more than the euro cylinder. Its mechanism follows the door edge, whereas the cylinder is the component worked with a key. Renewing the cylinder alone therefore keeps the existing handles, locking points, locking strip and gearbox, rather than replacing those parts.
Can I replace the cylinder without replacing the complete door lock?
Keeping the existing lock mechanism and changing its cylinder is often possible, as long as compatibility and correct operation are confirmed. A cylinder swap has limits, though. It will not fix an alignment fault in the door, handles that have worn or damage within the gearbox.
Can I identify a door lock from the key alone?
Treat the key as a clue rather than a full identification. Its profile or brand may suggest which cylinder or mechanism is involved. Usually, though, it cannot confirm the complete lock's model, measurements or security standard; door-edge photographs and visible identifying marks are more helpful.
What if there is no brand name visible on the lock?
It may still be identifiable without a maker's name. Photograph the handles and keyhole, plus the door edge and frame keeps, and record every number or symbol even if it seems unrelated to branding. The lock's dimensions, shape, operation and locking-point layout offer further identification clues.
Does a five-lever lock automatically meet BS 3621?
No, lever count does not prove that a lock meets BS 3621. Compliance belongs to the tested assembly, rather than internal lever numbers, bolt length or brand familiarity. For thief-resistant mechanical single-point assemblies, BS 3621 sets performance requirements with keyed locking and unlocking from both sides. Opening inside without a key may bring another standard into play, since BS 3621 covers keyed egress. Older markings may cite predecessors to BS 3621:2017+A1:2024, the current edition. Verify the exact model, full visible reference and relevant certification mark using original documents. Compliant locks normally carry the reference on product or packaging, often alongside certification.
How can I tell whether my door has a deadlock or a sashlock?
Examine the bolt and latch arrangement to separate the types. Deadlocks use a key to work a bolt without any handle-controlled latch; sashlocks pair a deadbolt with a spring latch and normally feature handles and a keyhole. For further identification, check door material before locating the lock on the surface or within the edge. Consider handles, keyhole, faceplate and locking-point count when distinguishing nightlatch, multipoint, mortice and cylinder designs.
Why does my lock work when the door is open but not when it is closed?
This often points to the latch, bolt or multipoint locking points failing to line up with the frame keeps. Check whether the door has moved, the hinges are worn or the alignment is poor before concluding that a replacement lock is needed.
Can a locksmith identify my lock from photographs?
The broad lock type can often be identified from photographs, which may also suggest a manufacturer or model. An exact compatibility decision may still depend on inspecting or measuring the parts. Mortice cases and the gearboxes used in multipoint locks particularly warrant that distinction.
What should I do if the door is locked and I cannot identify the lock?
Pause attempts to open the unidentified lock. Do not drill into it, use prising tools or keep forcing either the key or the handle. A qualified locksmith can be asked to identify the fitting and advise on the next step with the locked door.