Everything you need to know about mortise locks: types, installation and dimensions


 In this article, you will learn what types of mortise locks there are and what areas of application they are suitable for. You will also learn everything you need to know about the structure and function of mortise locks, the most important dimensions so that you can determine the right mortise lock for your door and other important tips.

about mortise locks: types, installation and dimensions

1. Basics

Mortise locks are the most common form of door lock today. You can find them in every apartment and room door. 
They are inserted into a rectangular recess that is milled into the door leaf. Mortise locks are only visible on the front edge (also called the closing edge) of the door leaf when the door is open. 
In contrast, there are screw-on or box locks that are mounted on the outside of the door leaf and are therefore also visible when the door is closed. Image of mortise lock vs. screw-on lock

Mortise locks are available in different sizes and designs. They can be used on both interior and exterior doors. Important points when choosing the right mortise lock are:
  • the right dimensions
  • the right type
  • the right safety class
We will discuss these points in more detail below.

2. Structure of a mortise lock

Let's first take a quick look at the structure of a classic mortise lock so that you become familiar with the technical terms. The further information in this article builds on this. 

A mortise lock usually consists of the following parts:
  • Faceplate: Open a door and look at the narrow side of the door leaf from the front. There you will see the so-called faceplate. This is the name given to the sheet metal that remains visible from the mortise lock when it has been installed in the door. In the faceplate, you will usually find a drill hole at the top and bottom. The mortise lock is fixed to the door leaf via these. The latch and the bolt also protrude from the faceplate.
  • Latch: This is used to lock the door. It snaps into place when the door is closed and prevents the door from opening accidentally. The latch can be released, for example, by operating the door handle so that the door can be opened. The latch only closes the door but does not lock it.
  • Deadbolt: If you look at the faceplate from the front, the lock deadbolt is usually located below the latch. It is usually operated with a key. If you lock a door with a key, the deadbolt is pushed out of the mortise lock and into the strike plate. The door is now locked. If you unlock the door again with the key, the deadbolt is essentially retracted and the door is unlocked.
  • Strike plate: This is the counterpart to the mortise lock. While the mortise lock is set into the door leaf, the strike plate is set into the frame (colloquially also often referred to as the door frame). It accommodates both the latch and the bolt via two openings and thus enables the door to be closed and locked.
  • Handle nut: Refers to the round opening in the mortise lock which accommodates the square of the door handle. The square is a metal pin with a square cross-section which is pushed into the handle nut. For interior doors, a door handle is usually pushed onto the square from both sides of the door leaf. For exterior doors, however, a fixed doorknob is often used on the outside of the door leaf. The nut spring ensures that a door handle moves back up after being operated, thus extending the latch out of the door leaf.
  • Lock base and lock cover: These metal sheets together form the so-called box of the mortise lock. It is located behind the faceplate and is no longer visible once the mortise lock has been recessed into the door leaf.
mortise locks

3. The most important dimensions

To ensure that you are really happy with your newly purchased mortise lock, you should make sure that you buy the right size. Mortise locks are standardized, but there are different sizes. You need to know what size you need for your door so that the lock fits.

Mortise depth: The mortise depth refers to the distance from the front edge of the mortise pocket (in the door leaf) to the deepest point of the pocket that accommodates the mortise lock. The mortise depth is usually measured in millimetres. Understandably, the mortise lock box must not be larger than the mortise pocket in the door leaf.

Backset: The distance between the centre of the keyhole (and the square pin) and the outside of the faceplate is called the backset. If you want to replace your existing mortise lock, the backset is particularly important. Only with the correct backset can you ensure that the door lock (e.g. profile cylinder or warded lock) and square are in the designated places and are thus congruent with the recesses provided for them in the door leaf.

Distance: If you already have door fittings and are looking for the right mortise lock, or conversely need the right door fittings, the distance is an important factor. It describes the distance between the centre of the square and the centre of the locking cylinder. For front doors or doors that use a profile cylinder, this distance is usually 72 or 92 mm in Germany, and usually 88 mm in Austria. For interior doors with a deadbolt lock, the distance is usually 72 mm in Germany and 90 mm in Austria.

4. What types of mortise locks are there?

Mortise locks are usually available in the following variants:

With profile cylinder hole (PZ hole): This variant is suitable for external or front doors, as a profile cylinder can be installed in it. In contrast to the warded lock, this offers significantly more security against burglary.

Profile cylinders are usually also equipped with a so-called change function. What does that mean? You open a traditional room door by pushing the door handle down. However, this is not possible with a front door with a fixed knob on the outside. In order to be able to open this without a door handle, there is the so-called change. This allows you to release the latch with one final turn of the key and thus open the door.

With warded hole: This variant is suitable for interior doors that can only be locked with a warded key. Warded keys are the classic room door keys.

These types of locks are very insecure and therefore not suitable for external doors. They can be picked, i.e. opened, relatively easily, for example with a lock pick. However, this can actually be an advantage for interior doors, for example, if a small child has locked themselves in.

With bathroom latch: With this variant, the door is not locked with a key, but with a rotary knob on the inside of the door (or the door leaf). For safety reasons, however, there is a device on the outside that allows the door to be opened from the outside in an emergency using a hexagon key or pliers.

5. What else do you need to pay attention to when choosing the right mortise lock?

Another important factor is the direction in which the door opens, i.e. the door stops. You can find out how to tell which stop your door has in our detailed door guide in the section “How to determine the door stop correctly”.

In summary, there are two standardized types of stops:

  • Doorstop DIN right
  • Door stop DIN left
Make sure that your mortise lock is designed for the correct door stop. Many mortise locks today have a rotating latch and can therefore be used on both sides, i.e. for both types of stop.

Also important are the different security classes, which differ significantly in their protective functions. We will discuss these in more detail in another article shortly.

We hope that this little guide has helped you to make a decision when buying your next mortise lock. Do you have any questions or would you like to add something? Please let us know in the comments!

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