The size of cylinder you need is determined by the thickness of the door and handle combination, for this reason there are many sizes available and you will need to be careful that you measure the cylinder accurately (one size will not fit all). It is possible to measure a door cylinder in the door, but to be sure it's best to remove it first.
Your new door cylinder should protrude by no more than 5mm from the handle back plates.
Measurement A - Measure from one end of the cylinder to the middle of the central screw hole.
Measurement B - Measure from the other end to the middle of the central screw hole.
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