How to measure a Cylinder Lock

Friday, 4 June 2021

Finding the Right Size Cylinder
You don’t need any special tricks or tools to accurately measure a cylinder size, you can do this simply with a metric ruler by taking the existing cylinder out of the door and measuring, this only takes a few moments and gives the most accurate measurement. Some are known to use there expert eye and measuring from the outside face of one backplate to the other but it is not something we would recommend for an accurate measurement. 

Measuring from Existing Cylinder
Before you remove the cylinder for an accurate measurement, double check that the existing cylinder does not stick out significantly from the handle backplate. Ideally, it should sit flush or just slightly protruding, ideally no more than 5mm.

Many cylinders are held in place by a Fixing Bolt that is screwed from the door edge through a threaded hole on the side of the cylinder under the cam. The cylinder size required is determined by the distance from each edge of the cylinder to the centre of the Fixing Hole.

Mark Long Cylinders - If the existing cylinder sticks out more than 5mm, use a pencil to mark on the cylinder the point that it leaves the backplate. This mark should then be used for measuring, rather than the end of the over sized cylinder.

Remove the Euro Cylinder - If you are unsure, instructions on next page.

Lay the Cylinder Down - Place cylinder on a flat and level surface on it’s side for measuring.

Measurements -
(A) Measure from the left end of the cylinder to the centre of the Fixing Hole. 
(B) - Measure from the centre of the Fixing Hole to the right end. 
If you marked the side of the cylinder with a pencil, then measure to the mark rather than the end.

Check Measurements -
(C) Measure the overall length required, either from end to end or between pencil marks. The overall length should then equal the sum of measurements (A) and (B).

Measuring to the Fixing Hole is the most common method of measuring cylinders.  However some people do not include the 10mm cam space in the centre of the cylinder. 
Therefore, they would refer to the example above as 30/10/30 (70mm overall).  Always check with supplier when placing an order.

Removal of Existing Cylinder
To remove the cylinder you will require a cross-head screwdriver to release the Fixing Bolt, which is visible just under the latch on the edge of the door.

Open the Door - Insert key to unlock and open the door. Leave key in lock. 

Remove Fixing Bolt - The cylinder is held in place by a long threaded bolt/screw. 
The head of the screw is visible under the latch on edge of the door.

Pull Cylinder Out - Turn the key while applying slight pressure to the opposite end of the cylinder. 
As you do this the cam will line up with the rest of the lock and you can slide the cylinder out. 
The key is usually turned approximately 25° clockwise or anti-clockwise.

Fitting a New Cylinder
Fitting a new cylinder is the back steps of the removal process.

Align Cam and Cylinder - Insert the key and turn until the cam is no longer sticking out and is lined up with cylinder.

Insert Cylinder - Holding the key and cylinder, guide through the cylinder cut-out on the door.

Fit Fixing Bolt - Insert Fixing Bolt through hole in the door edge and feel to locate the cylinder Fixing Hole. When it feels like the Fixing Bolt has found the Fixing Hole, screw the bolt until it and the cylinder is secure.

Download PDF doc of How to Measure a Cylinder Lock

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Welling Architectural Ironmongery Ltd
Welling Architectural Ironmongery

Glass and Timber Door Ironmongery Specialists

Call Sales Team  01451 824110