Types of mortice locks.

Identification guide (Yes it has a c not an s).

If you have an external wooden door fitted to your property the chances are you will also be the owner of a lever mortice lock. There are 2 main types of mortice lever locks used in the UK. Deadlocks and sash locks.

What are mortice Locks?

Firstly we need to clear up some definitions of this type of lock as it can get complicated if you are not familiar with the terminology. In the UK we tend to use mortice locks that are very similar in design to those used for a couple of centuries.

Mortice locks are fitted internally (rebated) to the leading edge of the door and are operated by a key.

Once the key is removed the lock is either deadlocked open, or deadlocked closed.

When you look at the front of a lock it will in 90% of cases tell you how many levers the lock has internally that the key has to operate to open. Mortice locks over the years have used any number of levers from 2 to 7. The standard on external doors is 5 and internal 2 or 3.

Dead lock or deadlock

This is a Union Strongbolt deadlock, (fig. 1). It is a 5 lever, curtained, mortice, BS3621 deadlock.

It is similar internally to both a Yale Deadlock and an ERA deadlock.

Let us explain this a little better. It is called a deadlock because once the key is removed it stays locked or open until the correct key is used to make it function again.

It is known as a mortice lock because it fits internally into a wooden or composite door in a space created for it, almost like a wood sandwich.

When viewing it externally you see a key slot with an escutcheon (keyhole). You will possibly not even know its colour as locks normally have a faceplate covering them.

We can tell it is curtained as the keyway is protected by a cut circular disc, known as a curtain (the silver semi circle at the top of the keyway). Curtains are included on lever locks to ensure that any lock assailant cannot easily get access to the levers that allow the lock to open.

5 lever refers to the number of levers which need to be manipulated by the key to get the lock open.

In the image fig.1, you will spot that it has an armoured plate like extra piece of metal stuck on that looks about the size of a post-it stamp. This plate is made from hardened steel and renders the lock practically undrillable. The hardened plate together with the curtain means that the lock is more than likely BS3621 (British Standard) approved. This can be checked by looking at the faceplate of the lock where the bolt protrudes it will have a British standard heart and will be marked as BS3621.

Confused yet? You can get the same lock without the armoured plate and this is known as a 5 lever curtained deadlock. These are usually fitted to internal doors, they are not insurance approved.

There are also 3 lever and 2 lever deadlocks that look similar, however they do not usually come fitted with a curtain (although rarely some do). And they do not usually come with any hardplate.

A locksmith should be able to manipulate two and three lever locks very easily if you lose the keys, beware of rogue traders.

Sash locks or sashlocks

Sash locks are deadlocks, but they also provide an extra function. They have a latch mechanism incorporated which means when closed without being locked , the door will stay shut until someone presses a handle to open it.

Generally, the latch is not lockable, therefore the bolt needs to be thrown independently to make the door secure.

It is not recommended to leave the door on the latch at night or at times when you are not in attendance.

Latches are normally wedged shaped and spring loaded so that they can close easily if the door is pushed to, without having to use a handle to secure the latch.

As above with deadlocks, they can be high security to low security. They can be 5 lever BS3621 fig.1, 5 lever non British Standard (fig. 2) or internal low security locks with just 2 or 3 levers.

The majority of internal parts of the sash lock will be very similar to the deadlock of the same brand.

Sash locks always require a longer section cut out of the door as in general they are around another 1/4- 1/3 taller than a deadlock due to the height of the latch. See fig. 3

Mortice Locks and Key Backsets

The final thing to say about UK mortice lever locks, if you need to replace one in your home, do not forget to measure the backset of your lock.

Backest is the distance from the face of the lock to the centre of the keyway.

In general, there is no formal size for ‘key backset’ on deadlocks, manufacturers can differ. Although there are common sizes, mostly based on old Imperial measurements.

The deadlock shown in fig. 3 has a backest of 76mm or 3″, therefore the keyhole will be further back from the edge of the door than the keyhole for the sash lock key hole shown above it.

The sash lock is a 64mm backset or 2 1/2″. The reason for the choice available is that different doors have mouldings and apertures that necessitates that handles sit back further from the door jambs.

It was quite common 20 years ago to regularly find 2″ or 50mm backet locks but these have declined in popularity mostly because they are not fit to become BS 3621.

This is because of the bolt throw they offer. Also, the mortice hole they fit into is narrow and they are susceptible to a well placed kick, the door would break or split more easily inside lesser quality wooden doors.

There are also larger locks still available that have 6″ backests.

This has been quite a difficult subject to explain to a third party. It is something that locksmiths do know about. Unfortunately it is also a bit like explaining the offside rule to someone who knows little about football. Hope it has added some clarity to helping you find the right mortice lock for your wooden doors.

If you spot anything missing please add a comment to make us aware and we will edit the mortice lock article.

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