What Is A Mortice Lock And How To Measure One

In this blog we will answer the most regularly asked questions about the most common type of door locking mechanism, the humble mortice lock. As with many ironmongery products, it’s not as straightforward as it may first appear so we will guide you through the typical types of mortice lock cases, lock terminology and the relevant measurements to take when replacing a lock or installing from new.

What is a Mortice Lock?

Mortice locks describe how the lock is installed to a door, not a function or how the lock is operated. A mortice is a recess or pocket cut into the leading edge of a timber or metal door. So, a mortice lock is a lock that is fitted into the recess rather than being surface mounted. Once fitted, the only visible part of a mortice lock is the forend, which can be seen when the door is in the open position. Mortice lock cases are available with various functions, the most common for external domestic properties are insurance rated 5 lever sashlocks and 5 lever deadlocks. A sashlock is a mortice lock which combines a beveled latch, operated by a pair of handles or doorknobs, and a key-operated deadbolt which locks/unlocks the door. A deadlock is operated only by a key, which throws a deadbolt into a keep on the door frame. On internal non-locking doors you’ll usually find a latch , which is a beveled, spring-loaded bolt that is used to hold a door in the closed position, and is commonly operated by a pair of door handles or knobs.

How Do I Know What Size My Lock Is?

When measuring an existing mortice lock, it is best to remove it from the door if possible. Before you reach for your tape measure though, we will need to cover some terminology so that the correct dimensions can be checked.

1. Lockcase – This is the main body of the mortice lock, often square or rectangular in shape. It houses all of the moveable components of the lock.
2. Forend - Also called the faceplate, whilst attached to the lockcase body, isn’t included when measuring the depth or height of the lockcase.
3. Follower – The part of the lock or latch which operates the bolt when turned by a spindle. The square hole is normally 8x8mm to suit a standard spindle. On a bathroom lock there is usually a second follower to accept a spindle from a thumbturn that controls the deadbolt, which is often 5x5mm. Another variant of the handle follower is a 9x9mm square follower, which is used on many escape function mortice sashlocks.
4. Piercing for the cylinder - This can be euro profile, oval profile, or dual profile; suitable for euro and oval cylinders. 
5. Keyway - If a lever operated lock key is being used you would refer to a keyway as the position where the key is inserted on 3 lever and 5 lever lockcases.
6. Bolt apertures – These will be around the area of the lockcase that is pierced for the cylinder, and around the handle follower. On commercial mortice locks, the lockcase is commonly drilled to accept 38mm bolt fixing furniture.

Important Lockcase Measurements

1. Backset – This measurement is found on both sashlocks and deadlocks. It is the horizontal distance measured from the outside face of the forend to the centre of the keyway or cylinder, or to the centre of the follower on a latch.
2. Centres – This measurement is found only on sashlocks. This is the vertical distance measured from the centre of the follower to the centre of the keyway.
3. Lockcase Depth – This is also referred to as case width and is the overall horizontal distance from the outside face of the forend to the back edge of the lockcase.
4. Lockcase Height – This vertical measurement does not include the forend of the lock, it is the overall height of the body of the lockcase only.
5. Follower - The measurement of the follower is usually the same as the backset on a mortice sashlock but on horizontal mortice locks it would be on the same plane as the keyway/cylinder aperture so would need to be measured in the same way that the backset is; the horizontal distance from the forend of the lockcase back to the centre of the follower.
6. Forend – Height and width. The forend is the part of the mortice lock or latch case through which the bolt/s protrude, and by which the lock or latch is screwed to the door. It can be radiused or square so when measuring, ensure the longest and widest parts are measured, not including the radius of the corners.

DIN lockcases differ from other types of lockcase e.g. lever locks and tubular latches, in that DIN families of locks all have the same case dimensions despite having different profiles or functions. So, the case of a DIN bathroom lock would have the same case height and case depth/width as a DIN sashlock or DIN escape lock. The forends will all have the same height and width, so you’d only need to confirm the function of the lockcase, profile of the cylinder e.g. euro or oval, and it’s always worth double checking the centres on bathroom and sashlocks as different variants are available to suit different door handles.

How Do You Measure a Tubular Mortice Lock?

So far, we’ve looked at large mortice lockcases, like insurance rated 5 lever sashlocks and DIN standard lockcases, but there are also smaller locks and latches which look very different to the above, larger lockcases. Small case locks and tubular latches and deadbolts use the same terminology as other locks but they’ll often have fewer components. For example, a tubular latch will have a forend, latch bolt and follower but wouldn’t have a piercing for a cylinder or key. A tubular latch is a compact and efficient latch, morticed into the door and operated by a pair of door handles or doorknobs, ideal for internal doors which need to be closed but aren’t locking. The important dimensions to check with a tubular mortice lock or latch are the lockcase depth and backset to the follower.

Specialist Mortice Locks

As we mentioned at the start, mortice locks have a variety of functions, and we’ve touched on how they can be operated, by cylinders or lever key, doorknobs and door handles, but there are other more specialist mortice locks that can be operated by panic hardware, a digital lock or access control. These less common types of mortice lock will still have the same aspects as we’ve discussed above, such as backset and centres, but may need more consideration when replacing to ensure compatibility with the other items of door hardware.

If in doubt, we’re on hand and you can contact us by phone, in branch or email and we'll answer any of your queries.