Fitting a mortice lock to a door is straightforward when you follow the More Handles guide. If you’ve recently bought a mortice lock or are adding one to a new door, our step by step guide shows you how to fit a mortice lock accurately and securely. There’s no need to hire a professional – simply follow our guide and add another feather to your DIY cap!

5 Lever Mortice Lock

Before you start fitting a mortice lock, make sure that you have all of the necessary tools to hand. You will need:


  • Mortice Lock
  • Pencil
  • Tape measure
  • Drill
  • Wood drill bits
  • Wood chisels
  • Mallet
  • Screwdrivers
  • Marking gauge or steel rule
  • Masking tape



Choose the right lock for you

There are various different types of mortice locks that are manufactured to different standards.

For external doors it is recommended that you use a 5 lever lock (BS3621) to conform to house insurance companies requirements.

For internal doors, 3 lever locks are sufficient.

These locks come in a variety of sizes and depths to suit different situations so be sure to check you are purchasing the right one, as once the alterations to the door has been made to fit the lock, it is very hard to change to suit a different lock.


Marking the door

If there has been a door previously fitted to the door frame that has had a mortice lock, it is easier to fit the mortice lock at the same height as the previous one as this will reduce the amount of work required when fitting the strike plate to the door frame.

Once you have decided at what height the lock is going to be situated you need to mark the door ready for drilling and chiselling.

Step 1: Mark a centre line down the edge of the door. With the mortice lock held up against the door at the height it is going to be, mark the top and bottom of the body of the internal mechanism and transfer these marks across the side of the door crossing the central line previously marked.


Preparing the door

Step 2: Measure the thickness of the housing of the internal mechanism and select a flat wood drill bit that is slightly thicker in diameter. DO NOT choose a drill bit that is wider than the front plate of the lock.

Step 3: Using the central line as a guide, drill a series of holes at a right angle to the side of the door, making sure the top and bottom holes are drilled using the position where the lines marked for the top and bottom of the internal housing cross the centre line as drilling points.

Step 4: These holes should be drilled to a depth deep enough so that the lock can be sunk in to the door and the front plate will lie flush with the side of the door. You can use a piece of masking tape wrapped around your drill bit as guide to help with this.

Step 5: Once the holes are drilled, use a sharp wood chisel and a mallet to remove the wood in between the holes leaving a rectangular hole big enough for the mortice body to slide into.

Step 6: Place the lock into the hole and mark around the front plate with a sharp pencil.

Step 7: With a mallet and a sharp chisel, chisel out a recess the thickness of the front plate so it will sit flush once fitted to the door.

Step 8: Carefully measure the position of the key hole and mark on the side of the door. You can do this by holding the lock up against the door or by using a paper template. If fitting a mortice lock with a latch, mark the centre of hole for the handle spindle also.

Step 9: Drill out the holes through the door using a drill bit and tidy up the keyhole using a hammer and chisel.

Step 10: Fit the mortice lock in place making sure to drill pilot holes for the screws to prevent splitting.


Fitting the strike plate

Step 11: Position the strike plate on the door frame ensuring the holes are lined up correctly with the bolt from the mortice lock.

Step 12: Mark around the outside of the strike plate and also around the inside catch areas.

Step 13: Chisel around the marked lines to the depth of the strike plate so it sits flush with the frame and chisel deep enough within the catch areas so the bolt can open out fully.

Step 14: Screw the strike plate in position remembering to use pilot holes to prevent splitting.


You should now have a neatly fitted mortice lock! If you found these instructions helpful or have any further suggestions to fit a mortice lock correctly, get in touch with us at More Handles.