Mortice door locks are one of the most common and secure ways to lock external and internal doors in UK homes. Whether you are upgrading a front door, fitting a new internal door or just trying to understand the difference between a sashlock and a deadlock, it helps to know what is going on inside the case.
This guide explains how mortice locks work and gives a detailed breakdown of all the parts in a traditional lever mortice sashlock and mortice deadlock, along with the frame components that make up the full locking system.
What Is a Mortice Door Lock?
A mortice door lock is a type of lock where the main lock body is cut into, or “morticed”, inside the edge of the door. Unlike surface-mounted locks, the bulk of the mechanism sits hidden in a rectangular pocket within the timber.
Traditional UK mortice locks are usually lever locks. Inside the case there is a stack of metal levers that must be lifted to the correct height by a specially-cut key. When the right key is used, the levers line up and allow the bolt to slide in or out to lock or unlock the door.
There are two main types used in domestic doors:
Mortice sashlock: combines a spring latch (for everyday closing) and a deadbolt (for secure locking) in one case, usually operated by a handle and a key.
Mortice deadlock: contains only a deadbolt and lever mechanism, with no latch or handle follower. It is generally operated by a key only and often used as an additional high-security lock.
| Lock type | Includes latch? | How it is operated | Typical use |
|---|---|---|---|
| Mortice sashlock | Yes – spring latch plus deadbolt | Handle for latch, key for deadbolt | Back doors, side doors, some front doors where you want a handle and key together |
| Mortice deadlock | No – deadbolt only | Key only (sometimes key outside, thumb turn inside) | Additional high-security lock on front doors and external doors |
How a Lever Mortice Lock Works
Lever mortice locks all share the same basic working principle. The details of the case and furniture vary between sashlocks and deadlocks, but the “engine” inside is very similar.
Core mechanism
At the heart of the lock is a lever pack. This is a stack of flat metal levers, each with a cut-out called a gate. A projecting piece attached to the bolt, known as a fence or stump, needs to pass through all these gates at once for the bolt to move.
When you insert the correct key and turn it, the shaped “bit” of the key lifts each lever to a specific height. If it is the right key, all the gates line up with the fence. The fence can then move freely, and the key’s turning action pushes or pulls the bolt in or out of the lock case.
If the wrong key is used, the levers sit at the wrong heights. Their solid sections block the fence from moving, so the bolt cannot retract or extend, and the lock remains secure.
Mortice Sashlocks: Parts and How They Work
A mortice sashlock combines two functions in one case:
The latch: a spring-loaded latch bolt that simply holds the door closed and is operated by the handle.
The deadbolt: a solid sliding bolt that secures the door when you lock it with a key.
External and visible parts of a sashlock
Lock case / body: the steel box morticed into the edge of the door. It contains the latch mechanism, deadbolt, lever pack and all the internal springs and linkages.
Forend / faceplate: the rectangular metal plate you see on the door edge. It shows the ends of the latch bolt and deadbolt and is fixed to the door with forend screws. The square follower hole for the handle spindle is also visible in this plate.
Latch bolt: the angled, spring-loaded “tongue” that projects from the lock case. When you close the door, the bevelled edge rides over the strike plate on the frame. Once it has passed the keep, a spring pushes the latch back out so it engages and holds the door closed.
Deadbolt: the solid rectangular bolt that slides further into the frame when you turn the key. Unlike the latch, it is not spring-loaded and will stay in the locked or unlocked position until moved by the key.
Handle / lever: the handle or lever on each side of the door that you push down or turn to retract the latch. Handles are usually mounted on a backplate or rose, which covers the spindle hole and fixing screws.
Spindle: the square metal bar that passes through the door and through the follower inside the lock case. It links the two handles together so that pressing either handle turns the spindle.
Keyhole and escutcheons: the keyhole in the door face, usually covered inside and out by decorative keyhole covers called escutcheons. The keyhole lines up with the lever pack inside the lock case.
| Part | Where it is | Main function |
|---|---|---|
| Lock case / body | Morticed inside the door edge | Houses latch mechanism, deadbolt, lever pack and internal springs |
| Forend / faceplate | Visible on the door edge | Finishes the lock neatly and exposes latch and deadbolt ends |
| Latch bolt | Protrudes from the forend | Holds the door closed under spring tension, operated by the handle |
| Deadbolt | Behind the latch in the lock case | Provides secure locking when thrown into the deadbolt keep |
| Handle / lever | On both faces of the door | Operates the latch via the spindle and follower |
| Spindle | Running through the door and lock case | Connects the two handles and turns the follower to retract the latch |
| Keyhole & escutcheons | Door faces, aligned with lever pack | Allow the key to enter and operate the levers, with decorative covers |
Internal parts of a sashlock
Follower (hub): a square rotating piece inside the lock case that the spindle passes through. When a handle is pushed down, the spindle turns the follower, and the follower pulls back the latch bolt via a retractor linkage.
Latch spring: the spring that returns the latch bolt to its extended position when the handle is released. This is what makes the door “click” shut and stay closed by itself.
Lever pack: several flat metal levers (often 3 or 5 in domestic locks) pivoting on a pin. Each lever has a gate, and together they form the main security element of the lock. Only the correct key can lift all the levers so that all the gates line up with the fence.
Lever springs: small springs that push each lever back down to its resting position when the key is removed. These ensure the lock “re-locks” internally and that the wrong key will not be able to move the bolt.
Fence / stump: a protruding part attached to the deadbolt or bolt carrier. The fence must pass through the aligned gates in the levers. If even one lever is at the wrong height, the solid part of that lever blocks the fence and prevents the bolt from moving.
Keyway and key guide: the internal passage that guides the key through the case and into the lever area. A key guide plate helps keep the key aligned so that the bit lifts each lever correctly.
Bolt thrower / cam / wheel: the mechanism that converts the turning action of the key into linear movement of the deadbolt. As you turn the key beyond the point where the levers are lifted, this cam pulls or pushes the bolt into the locked or unlocked position.
Anti-pick and anti-saw features (on higher security locks): some sashlocks include hardened steel inserts in the bolt to resist sawing, and special shapes or notches in the levers to make them harder to manipulate with lock-picking tools.
| Component | Role in the mechanism |
|---|---|
| Follower (hub) | Turns with the spindle when you operate the handle, retracting the latch bolt |
| Latch spring | Pushes the latch bolt back out after the handle is released |
| Lever pack | Set of levers that must be lifted to the correct height by the key for the bolt to move |
| Lever springs | Return levers to their resting position once the key is removed |
| Fence / stump | Engages with the gates in the levers; can only move when all gates line up |
| Keyway & key guide | Guide the key into the correct position to lift the levers |
| Bolt thrower / cam / wheel | Converts key rotation into linear movement of the deadbolt |
How a mortice sashlock works in practice
To close the door (not locked)
When you push or pull the door shut, the bevelled edge of the latch bolt runs up over the strike plate in the frame. The latch spring then pushes the bolt back out into the latch keep, holding the door closed. To open the door again, you simply push the handle down. The spindle rotates the follower, the follower retracts the latch, and the door opens.
To lock the door
To properly lock the door, you insert the key into the keyhole and turn it. As the key turns, the shape of its bit lifts each lever in the pack to a specific height. When all the gates line up with the fence, the fence is free to move. Continued turning of the key drives the deadbolt out of the case and into the deadbolt keep in the frame. Even if someone operates the handle and retracts the latch, the door cannot open while the deadbolt is thrown.
To unlock the door
To unlock, you insert the key and turn it in the opposite direction. The cam pulls the deadbolt back into the lock case. Once the deadbolt is fully retracted, the door can be opened again using the handle and latch as normal.
Mortice Deadlocks: Parts and How They Work
A mortice deadlock is a simpler, more focused version of a mortice lock. Instead of combining a latch and deadbolt, it contains only the deadbolt and lever mechanism. It is usually operated by a key from both sides and is often fitted as an additional high-security lock on external doors.
External and visible parts of a deadlock
Lock case / body: a compact steel box morticed into the door edge, housing the deadbolt and lever pack. Because there is no latch mechanism, the case is usually smaller than a sashlock case.
Forend / faceplate: the metal plate on the edge of the door which shows only the end of the deadbolt. It is screwed to the door and may include a marking or kite symbol on high-security models.
Keyholes and escutcheons: normally there is a keyhole on both sides of the door, each covered by an escutcheon. In some setups the outside is key-operated and the inside may be a key or a thumb turn, depending on the type of cylinder or lever arrangement.
| Part | Where it is | Main function |
|---|---|---|
| Lock case / body | Morticed into the door edge | Contains deadbolt and lever pack, no latch mechanism |
| Forend / faceplate | Visible on the door edge | Holds the case in place and exposes the deadbolt end |
| Deadbolt | Inside the case, projecting through the forend | Engages with the frame keep to securely lock the door |
| Keyholes & escutcheons | Door faces, aligned with lever pack | Allow the key to operate the levers; escutcheons tidy and protect the keyholes |
Internal parts of a deadlock
Deadbolt: the main locking bolt, usually with a longer throw than in a sashlock. On quality deadlocks, it often contains hardened steel inserts to resist cutting or sawing.
Lever pack: a set of levers (commonly 3-lever or 5-lever) forming the security core. As with a sashlock, the correct key must lift each lever so that all the gates align with the fence. Many British Standard deadlocks use five levers and enhanced designs for greater resistance to picking and manipulation.
Fence / bolt stump: the projecting part that must pass through the aligned gates. It is connected to the bolt, so if the fence cannot move because a lever is in the way, the bolt cannot retract or extend.
Lever springs: springs that push the levers down into their resting positions when the key is removed. These help ensure the lock is secure and ready to resist another attempt at operation.
Keyway and key guide: the internal channel that guides the key into the lever area. This keeps the key aligned so that its bit engages the levers correctly.
Bolt thrower / cam / wheel: the mechanism driven by the key that actually moves the deadbolt. As you continue to turn the key after the levers are correctly lifted, the cam pushes the bolt into the locked position or pulls it back when unlocking.
Case screws and cover plate: screws that hold the case together and a removable cover plate used by locksmiths or manufacturers for assembly, servicing and repair.
Security features: higher-quality mortice deadlocks may include hardened anti-drill plates around the keyway or on the forend, hardened pins and special lever shapes or notches designed to resist picking, drilling and other forced entry techniques.
| Component | Role in the mechanism |
|---|---|
| Deadbolt | Slides into and out of the frame keep to lock or unlock the door |
| Lever pack | Provides key-controlled security; only the correct key lifts all levers to align the gates |
| Fence / bolt stump | Moves with the bolt and must pass through aligned lever gates to allow bolt movement |
| Lever springs | Return levers to resting position after key is removed to keep the lock secure |
| Keyway & key guide | Guide the key into the correct position to engage the levers |
| Bolt thrower / cam / wheel | Translates the turning of the key into linear deadbolt movement |
| Security plates / hardened inserts | Protect the case and bolt against drilling, sawing and forced attack |
How a mortice deadlock works in practice
To lock the door
To lock the door, you close it and then insert the key into the keyhole. As you turn the key, its bit lifts each lever. When all the gates align, the fence is free, and continued turning of the key pushes the deadbolt from the lock case into the deadbolt keep in the frame. Once fully thrown, the door is locked, and the bolt will not move again until the key is used.
To unlock the door
To unlock, you insert the key and turn it the opposite way. The cam pulls the deadbolt back into the case. Once the deadbolt is fully retracted, the door can be opened, usually with a separate latch or nightlatch taking care of the everyday closing function.
Frame Components and Keeps
The lock case and mechanism are only half of the story. For a mortice lock to be effective, the door must close into a properly fitted frame with strong keeps and strike plates.
Strike plate / keep: the metal plate fixed to the door frame, with openings that receive the latch bolt and/or deadbolt. On a sashlock, this is often a combined keep with separate pockets for the latch and deadbolt.
Deadbolt keep / box strike: a deeper metal box recessed into the frame where the deadbolt enters. This gives the bolt something solid to bite into, greatly improving the strength of the lock under attack.
Fixing screws: the screws that secure the keeps to the frame. For real security, longer screws that bite into the solid timber of the frame and surrounding structure are essential, not just short screws into soft or damaged wood.
| Component | Works with | Main purpose |
|---|---|---|
| Strike plate / keep | Latch bolt and deadbolt | Receives the bolts and holds the door closed and locked |
| Deadbolt keep / box strike | Deadbolt only | Provides a deep, solid pocket for the deadbolt for improved strength |
| Fixing screws | Strike plates and keeps | Secure the hardware firmly to the frame, ideally penetrating into solid timber |
Sashlock vs Deadlock: Key Differences
Although they share many internal components, mortice sashlocks and mortice deadlocks play slightly different roles on a door.
Mortice sashlock: combines a spring latch and deadbolt in one case. The latch is operated by a handle or knob and simply keeps the door closed. The deadbolt is operated by a key and provides the actual security. Sashlocks are commonly used on back doors, side doors and some front doors where you want a handle and key in one tidy assembly.
Mortice deadlock: contains just the deadbolt and lever mechanism, with no latch or handle follower. The door is often closed by a separate latch or nightlatch and then locked with the deadlock for extra security. Deadlocks are commonly fitted as an additional lock on front doors, particularly where insurance-approved 5-lever or British Standard locks are required.
| Feature | Mortice sashlock | Mortice deadlock |
|---|---|---|
| Includes latch | Yes – spring latch for everyday closing | No – deadbolt only |
| Includes deadbolt | Yes | Yes |
| Handle required | Yes – to operate the latch | No – usually key only |
| Typical position on door | Main lock where handle and key are together | Secondary or additional high-security lock |
| Typical doors | Back doors, side doors, some front doors | Front doors and external doors needing extra security |
| Everyday use | Door held shut on latch, locked with deadbolt when needed | Door closed by separate latch/nightlatch, then deadlocked for security |
Summary
Mortice door locks may be hidden inside the edge of the door, but there is a lot going on inside the case. A stack of carefully shaped levers, a solid deadbolt, a spring-loaded latch and a set of springs and cams all work together so that only the correct key can move the bolt.
Understanding the names and roles of the parts in a mortice sashlock and mortice deadlock makes it much easier to choose the right lock, diagnose problems and talk confidently to locksmiths, hardware suppliers and tradespeople. Whether you are upgrading to a 5-lever lock, replacing tired hardware or planning a full door refurbishment, knowing what is happening inside the mortice lock is a big step towards a more secure, better-functioning door.
