Guide
Types of Door Locks in the UK: What Each One Is and Where It Fits
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Every UK Door Lock Type at a Glance
Ask anyone to help with a faulty or worn-out lock and one of the first things they will want to know is which type you have. The keyhole on its own seldom settles that. Start with the door instead: what it is made of, where the mechanism is housed, and what shows on the inside face and along the edge when it is open. Those clues are usually enough to separate a mortice lock from a nightlatch, a rim cylinder or a multipoint system.
Part of the muddle is in the names. Some locks are called after the whole mechanism and others after the piece the key goes into, so mortice lock, nightlatch, euro cylinder and multipoint lock get mixed up even though each one describes a different part or system. The matrix below lines up the main types found on UK doors, and the middle column is the quickest way in.
| Lock type | Normally found on | What you can see | What sets it apart |
|---|---|---|---|
| Mortice deadlock | Mostly timber front and back doors | A case sunk into the door edge, with a bolt showing when the door is open | A key throws the bolt, and there is no handle-driven latch in the same case |
| Mortice sashlock | Timber doors, both external and internal | A case sunk into the edge showing a spring latch and a separate bolt | Handles work the latch while the key works the locking bolt |
| Nightlatch with rim cylinder | Mostly timber entrance doors | A box fixed to the inside face, with its cylinder showing on the outside | The latch usually catches as the door shuts |
| Euro cylinder in a multipoint lock | Usually uPVC and composite doors | A euro-profile cylinder beside the handle and a long strip down the door edge | The key turns the cylinder while the wider mechanism drives several locking points |
| Euro cylinder in a single-point lock | Some timber, aluminium and metal doors | A euro-profile keyway with no long strip or extra locking points | The cylinder drives one central lock case |
| Surface-mounted rim lock | Some older timber doors, internal doors and outbuildings | The whole lock case sits on the inside face | It is fixed to the surface instead of set into the edge |
Each row names a lock family, not a model. A modern timber door may carry a multipoint, and aluminium or metal doors may use a cylinder-operated case, so the material column is a guide rather than a rule. Selecting any replacement part still requires markings and measurements first. The rest of this guide covers how to recognise each type, what its main components do and where the useful markings are, and explains why looks alone cannot confirm the exact model or security standard. The two middle columns are where most people go wrong, which is why each has its own section below.
Locks Fitted in a Timber Door
Mortice Deadlocks and Mortice Sashlocks
When the keyhole sits in the edge of a timber door, the lock is a mortice. A deadlock gives you a bolt worked by the key and no latch. A sashlock adds a latch for the handles.
Nightlatches With Rim Cylinders
When the key goes through the face of the door and into a box on the inside, the lock is a nightlatch with a rim cylinder. It usually latches whenever the door closes. Not every box on the inside face is a nightlatch, though. A traditional rim lock fitted there may contain a latch, a bolt or both, depending on its design; it may not latch automatically, and it may be operated by a key, a handle or a knob.
Reading the Whole Door
Timber doors commonly carry a mortice lock, a nightlatch, a surface-mounted rim lock, or two separate systems together, and in most cases the deciding question is whether the case sits inside the edge or on the inside face. Where a timber entrance door has both a nightlatch and a separate mortice lock, the two operate independently and should be identified one at a time. They are not ranked against each other; they simply do different jobs. Some timber doors take a multipoint too, a complete system of connected parts more often found on uPVC and composite doors, in which locking points along the door edge move into keeps on the frame.
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 Type Belongs on Each Door
A door's material and use decide what lock it carries; the lock never decides the door.
Two Exceptions
First, timber doors are now manufactured with multipoints too, so a door's age matters more than its material alone. Second, a flat entrance door onto a shared corridor needs separate thought about how people get out; where its lock opens from inside without a key, a different standard may apply.
Narrowing Down, Not Diagnosing
Knowing the lock family helps, but it confirms neither the faulty part nor what should replace it. Even when locks share the same outward appearance, their size, function, security and compatibility can vary. Before ordering, work through four questions: identify the family, markings and operation; find the cause, since a lock that will not engage may involve the cylinder, case, gearbox, spindle or alignment; decide whether one compatible component or a door adjustment would do; and make sure the replacement fits, operates reliably and secures the entrance. "Euro cylinder" and "five-lever sashlock" are too broad for choosing a part, because measurements, handing, faceplate shape, fixings, case dimensions and connected hardware all matter. Brands and labels are not proof of a standard; certification applies to a specific product, so check the full reference and model. If the cause or the right part is unclear, arrange an inspection first; it can avoid a full lock change you did not need.
- Timber entrance doors normally have a mortice lock and often a nightlatch too.
- uPVC and composite doors normally have a euro cylinder working a multipoint strip.
- Aluminium doors normally have a multipoint or a cylinder-operated case.
- Internal timber doors usually have a lighter mortice latch or sashlock.
- Some older timber doors and outbuildings have a surface-mounted rim lock.
Reading a Lock's Name
Read a lock listing left to right and it explains itself. In [Maker] five-lever mortice sashlock, the first word names the manufacturer, the second gives the number of levers, the third says the case is recessed into the door, and the fourth says it has both a latch and a deadbolt. Other listings add the case size, the finish or a security standard. These are separate facts about separate things, so recognising one term never confirms the complete specification. Note what is missing from the example: a five-lever mechanism does not in itself demonstrate compliance with BS 3621.
What Lever Counts Actually Mean
A lever-operated mortice lock has a set of internal levers that the key lifts to specific heights before the bolt can move, three in a three-lever lock and five in a five-lever lock. The count helps describe the mechanism but is not a full security assessment: locks with identical counts can differ in materials, construction, bolt design, attack resistance and tested performance. Three-lever locks are often fitted to internal doors, and five-lever locks are common on external timber doors, but the count alone should not be used to confirm suitability for an entrance door or an insurer's requirements.
Words and Measurements in a Listing
Mortice and rim say whether the case is recessed or surface-mounted. Deadlock means a bolt without a spring latch; sashlock means a deadbolt plus a handle-operated latch; nightlatch means a surface-mounted lock that normally latches when closed. Cylinder is the key-operated component; multipoint is a mechanism with locking points along the edge. Case size gives the mortice case's overall depth, backset the distance from the faceplate edge to the keyhole, cylinder or spindle centre, and finish the surface, for instance brass, chrome or satin nickel. These narrow the search without proving a part will fit.
The Faceplate Marking
Start with parts visible while the door is open; a mortice or multipoint faceplate may be stamped with a maker's name, logo, series or code. Handles carrying one maker's name may sit over another company's lock. Do not remove a lock case, gearbox or strip to look for numbers, and check type and measurements before ordering.
Types You Are Less Likely to Meet
Beyond the main families, several other types appear on UK doors, and most of them work alongside a primary lock.
Door bolts
surface-mounted and operated manually, add a second point of fixing.
Hinge bolts
protect the hinge side of a door against being forced.
Push-button (mechanical digital) locks
use a code instead of batteries, wiring or an app. You will see them on offices, storage rooms, communal areas and some residential side doors. A numbered keypad sits outside and a knob, lever or thumbturn inside; entering the code releases the handle so it can move the latch or case. A separate tubular latch, mortice latch or lock case may have a connection to the keypad. For identification, take photographs showing the door from both sides, its edge faceplate and any markings on the keypad housing.
Sliding patio door locks
differ from those on hinged entrance doors. They are built into the handle assembly or linked to a mechanism inside the vertical edge of the sliding panel, and may use a single hook or bolt, multiple hooks, a key cylinder, a handle and thumbturn, an anti-lift device and keeps on the meeting frame or fixed panel. Identify one from the handle shape, fixing positions, cylinder profile and faceplate, and record any stamped name or number.
Window locks
form a separate family with dedicated fittings.
This guide does not cover electronic or smart locks, access control or master key suites, and none of those is part of our work. The table at the start of this guide summarises the rest.
Not Sure What Lock You Have? Ask Us
An odd door is exactly the kind of call we are happy to take. Describe it and we will identify the lock, set out what changing or repairing it involves, and quote before work starts.
Useful to have: the door's material, the position of the keyhole, and a clear photo of the faceplate with the door open. Please do not close an open door just to show us the fault.
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Door Lock Type Questions
How can I tell what type of door lock I have?
Start by checking the material of the door and then locate the lock, either embedded in the edge or fixed to the surface. Handles, the key opening, the faceplate and the locking-point arrangement help distinguish cylinder, mortice, multipoint and nightlatch designs. If a key works the bolt but handles operate no latch, it is a deadlock. A sashlock also contains a spring latch, so handles usually sit alongside its keyhole.
What type of lock is usually fitted to a uPVC door?
On most modern uPVC entrance doors, locking is handled by a multipoint mechanism with a euro cylinder and handles. Its name refers to the wider system. Alongside the cylinder are the hooks, gearbox and locking strip, together with keeps located on the frame.
How do I know if I have a mortice lock or a nightlatch?
The body of a nightlatch is visible inside the door, mounted on its face; a mortice mechanism is inset into the edge. A timber entrance door can have both. Check the other fitting position as well, even once one lock has been recognised.
Is a euro cylinder the same as a multipoint lock?
A euro cylinder is not a multipoint lock: it provides the key-operated component within the system. The multipoint mechanism occupies the door edge. Fitting another cylinder changes that part alone; the handles and locking strip remain, as do the gearbox and locking points.
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?
A key on its own will usually leave identification uncertain. Its brand or form might suggest a mechanism or cylinder, while the full model, dimensions and security standard remain unconfirmed in most cases. Photographing the edge of the door and visible marks gives better information.
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: five levers describe the mechanism, which does not establish BS 3621 compliance. The performance standard tests thief-resistant, mechanically operated single-point assemblies requiring keys to lock and unlock from either side. Compliance concerns the tested assembly, not lever count, bolt length or a recognisable brand. BS 3621:2017+A1:2024 is current; older locks may show earlier editions. Check the exact model, full reference and certification marking against original documentation. Compliant products normally show BS 3621 on the lock or packaging, often with a certification mark. If inside opening needs no key, another standard may apply because BS 3621 covers key-operated exit.
How can I tell whether my door has a deadlock or a sashlock?
A bolt operated by a key, without a handle-controlled latch, points to a deadlock. A sashlock includes a sprung latch as well as the deadbolt, normally explaining the presence of handles and a keyhole. First note the door material for broader identification, then check for edge-inset or surface mounting. Study the keyhole, handles and faceplate, and count locking points to distinguish cylinder, mortice, nightlatch and multipoint arrangements.
Why does my lock work when the door is open but not when it is closed?
The lock may be meeting the frame incorrectly when the door closes. A latch, bolt or multipoint locking point that misses its keep often explains this pattern. Door movement, hinge wear and poor alignment deserve checking before deciding to replace the lock itself.
Can a locksmith identify my lock from photographs?
Yes, photographs can often reveal the type of lock and may point towards its manufacturer or model. Choosing an exactly compatible part can require more information, though. For mortice cases and multipoint gearboxes in particular, measurements or an inspection may still be necessary.
What should I do if the door is locked and I cannot identify the lock?
Stop forcing the key or handle, and avoid drilling or prising at the lock. If the door remains locked and its mechanism is unknown, leave further attempts there. Ask a qualified locksmith to identify the fitting and advise on how to proceed.