Euro Cylinder Guide
How to measure my door lock euro cylinder?
To measure your euro cylinder you simply need to measure from the centre screw hole to the outside edges. This will give you two sizes which makes up the size of your door lock. The two sizes should equal the overall length of the cylinder. So a 40/40 would be 80mm in total length.
The measurements for A and B should equal C if you measured your cylinder correctly.
Do cylinders have an internal and external side?
Most standard euro cylinders which use a key on both sides do not have a specific internal or external side. They are reversible and can be installed any way round.
Thumb turn cylinders which use a thumb turn knob on the internal side of the cylinder do have a specific sides. When measuring a thumb turn cylinder you must ensure you make note of which size of the two sizes is the internal side.
High security cylinders may also have a specific external side. This is because all of the security features will be installed on the external half of the cylinder. So when looking to replace your cylinder to a high security cylinder, double check to see if that cylinder has a specific external side.