Mortice, Cylinder and Multipoint Locks: What's the Difference?

Why the lock type matters

When you describe a lock problem, the first thing a locksmith wants to know is what kind of lock it is. The type decides how the lock fails, which parts can be replaced on their own, what the replacement options are, and what details are needed to order parts. It also explains why advice that works for one lock (say, changing a cylinder after keys go missing) doesn't apply to another (a lever mortice lock has no separate cylinder to change).

Most homes and offices in Sandton have a mix: lever mortice locks on older timber doors, cylinder locks on many aluminium and newer doors, multipoint locks on some front and patio doors, rim nightlatches, and hook locks on sliding doors. This guide covers the three types people most often ask about. Sliding-door hook locks and padlocks work differently and aren't covered here.

Mortice locks

A mortice lock sits inside a rectangular pocket (the mortice) cut into the edge of the door. Only the faceplate on the door edge, the keyhole and the handles show. As Wikipedia's article on the subject puts it, "mortise lock" describes only a method of fitting the lock and says nothing about its quality or key mechanism.

Deadlocks and sashlocks

• A mortice deadlock has a single key-operated bolt and no handle-operated latch. The door is held shut only when it is locked.
• A mortice sashlock combines a sprung latch, worked by the handle, with a key-operated deadbolt. You can open and close the door with the handle and lock it with the key when you need to.

Lever or cylinder mechanism

Most traditional mortice locks use levers: flat plates inside the case that the key's bit has to lift to exactly the right heights before the bolt can move. In South Africa, lever locksets are widely sold with two, three or four levers; ASSA ABLOY's South African range, for example, includes two-, three- and four-lever Union locksets carrying the SABS mark. More levers generally means more possible key differences. The UK's BS 3621 standard, which Union describes as the basic thief-resistant standard for external residential doors in the UK, calls for five levers on lever locks along with minimum bolt throw and attack tests.

Other mortice lock cases are made to take a cylinder instead of levers, usually a euro-profile cylinder. Those combine the mortice body of one type with the key mechanism of the next.

Typical mortice lock problems

Lever locks are sensitive to worn keys and to a bolt that drags on its strike plate. Because the levers are inside the case, a lever lock with lost keys can't be "re-keyed" just by swapping an external part. Mortice locks also need a door thick and solid enough to take the pocket: Wikipedia notes that cutting the mortice weakens a typical timber door, which is why the fit of the lock in its pocket matters.

Cylinder locks

A cylinder is a self-contained key mechanism. Inside it is a plug that turns only when the right key lines up a set of pins or other tumblers. At the back of the plug a cam or tailpiece transfers that turn to whatever bolt mechanism the cylinder drives.

Common cylinder formats

• Euro-profile cylinders have a round body with a narrower "tail" below, and pass right through the door and lock case. They are held in place by a single screw through the lock's faceplate. Common versions are key on both sides, or key outside and thumbturn inside. Wikipedia notes that a euro cylinder can be changed without altering the boltwork.
• Oval and other profiles work on the same principle with a different cross-section. A replacement must match the profile exactly.
• Rim cylinders are fitted from the outside face of the door and drive a lock (often a nightlatch) screwed to the inside face.

How cylinder security is graded

The European standard EN 1303 grades cylinders with an eight-digit code. According to ASSA ABLOY's technical summary of the 2015 edition, the digits cover things such as durability (25,000 to 100,000 test cycles), corrosion resistance, key security (grades 1 to 6) and attack resistance (grades 0 and A to D, where D is the highest). In the UK, TS 007 and Sold Secure SS312 add further attack tests; Secured by Design lists both as standards for replacement cylinders. Snapping, a forced attack on the cylinder, is one of the risks these attack ratings address, which is also why a cylinder should not stick out far beyond the handle or escutcheon.

Typical cylinder problems

Dirt and grit in the keyway, worn keys, a cam that has broken or slipped, and a cylinder clamped too tightly by over-tightened handles or a fixing screw. Because the cylinder is separate, it can often be replaced on its own when keys are lost or the cylinder is worn.

Multipoint locks

A multipoint lock bolts the door to its frame at several points rather than one. It has a long faceplate running most of the height of the door edge, with a central lock case (often called the gearbox) behind the handle and cylinder. A locking bar inside the faceplate connects the gearbox to the extra locking points above and below.

The locking points vary by make and model: hooks, rollers, mushroom cams, deadbolts and shootbolts, or a combination. Each engages with its own keep on the frame.

How it's operated

On most residential multipoint doors you close the door, lift the handle to throw the hooks or bolts into their keeps, then turn the key to lock them in place. Some designs lock automatically. MACO's user manual for its door locks makes an important point: a closed but unlocked door only has a "shielding function". The security, weather sealing and other properties are only achieved when the door is locked.

Secured by Design lists PAS 3621 and PAS 8621 as the multipoint equivalents of the BS 3621 and BS 8621 lock standards in the UK.

Typical multipoint problems

Multipoint locks rely on the door sitting accurately in its frame, with the seals compressed just enough. If the door drops, swells or the keeps move, the handle becomes hard to lift and people start forcing it. MACO's manual warns that excessive force on the handle damages the handle or the lock mechanism. A gearbox that has failed internally can leave the handle floppy or the door stuck locked. On some makes the gearbox can be replaced without changing the whole locking bar, provided an exact match is available.

The three types side by side

How to tell which lock you have

These checks only involve looking and using the lock normally. Don't remove screws or parts.

• Look at the door edge. A short faceplate around the bolt suggests a mortice or cylinder mortice lock. A faceplate that runs most of the height of the door, with extra bolts or hooks, means a multipoint lock. A metal box screwed to the inside face of the door is a rim lock.
• Look at the keyhole. A keyhole shaped like a round hole with a slot below it, taking a key with a bit, is a lever lock. A small, flat slot in a round or euro-shaped body is a cylinder.
• Look at the key. Lever keys have a shaft with a flag-like bit. Cylinder keys are flat blades with cuts or dimples.
• Try the handle. If you have to lift the handle before the key will lock, it's almost certainly a multipoint lock.
• Look for markings. A brand name, model or standard mark is often stamped on the faceplate, and sometimes on the key bow or the cylinder face. Photograph it.

Things that make problems worse, and when to call

Call a locksmith if the lock is getting harder to operate, if the key turns without moving the bolt (see key turns but the door won't unlock), if a multipoint handle has gone floppy or won't lift, if there are signs of tampering, or if you no longer know who has keys. Our guide to lock repair versus replacement explains how the next decision is made, and when a new lock is needed see lock replacement in Sandton.

To help a technician identify the lock before a visit, send photos of the door edge faceplate (close enough to read markings), the inside and outside of the door, the key, and the keeps or strike plate on the frame. Say what the door is made of and describe exactly what happens. A mobile locksmith in Sandton can then bring suitable parts or tell you if something has to be ordered.

Need a locksmith to look at it?

If this hasn't solved the problem, our lock replacement service covers it. We're a mobile locksmith in Sandton, so we come to your door.

Sources and further reading

• Wikipedia: Mortise lock — Definition, sashlock and deadlock, lever and cylinder mechanisms, effect of the mortice on a timber door
• Wikipedia: Euro cylinder (pin tumbler lock types) — Euro-profile, oval and other cylinder profiles; changing a cylinder without altering the boltwork
• ASSA ABLOY DACH: Technical requirements, DIN EN 1303 (PDF) — EN 1303:2015 eight-digit classification, including durability, corrosion, key security and attack resistance
• Secured by Design: Locks and associated hardware standards — BS 3621, BS 8621, TS 007, SS312, PAS 3621 and PAS 8621 summarised
• MACO: Operating and maintenance instructions for door locks, end users (Doc. 757585) — Multipoint operation by handle or cylinder, seal counterforce, closed-but-unlocked doors, damage from excessive handle force
• Lock Shop Direct: Multipoint lock measurement guide — Multipoint components: gearbox, hooks, rollers, mushroom cams, deadbolts and shootbolts; maker markings on the faceplate
• ASSA ABLOY South Africa: Union locksets — Two-, three- and four-lever and euro-profile locksets sold in South Africa with SABS approval
• Union: What are BS3621 locks? — Five-lever requirement, 20 mm bolt throw and key differs under BS 3621