Open your door and measure from the centre M5 screw on the side of the door, to the edge of your existing cylinder on the inside of your door. This is the 'B' measurement. For example, this might be 40mm. Put these two measurements together to get the right size - your B measurement goes first e.g. 40/50. It's important you choose the right size cylinder for your door, so it fits properly. To measure your cylinder: Then, measure from the centre M5 screw to the edge of your existing cylinder on the outside of your door. This is the 'A' measurement. For example, this might be 50mm

The new Yale 3 Star AS Platinum cylinder is independently tested by BSI to be awarded the British Kitemarked TS007:2014 3 star accreditation.Insert key into external side of cylinder and turn until revolving cam lines up with cylinder body.