How To Measure a Cylinder
Yale Cylinder - Technical Guidance
To measure your cylinder, you must first remove it. The cylinder is held in place by a single cross head screw. In the diagram below you can see the hole for the screw. To remove it , open the door and locate the head of the screw which is on the lock side of the door,it can sometimes look as if it is one of the screws holding the lock in place. Once you have located and removed the retaining screw. insert the key and turn to the positionshown below and then gently pull towards you with the key. If it doesn't move wiggle the key a little until the cylinder releases.
The size of a cylinder is measured from the centre of the screw hole to the outside face as in the diagram above. The reason we need to measure both sides (a+b) is that cylinders aren't always the same on both sides. You then order a cylinder of the sizes you measured eg 40mm/40mm
