If disctance A is 60mm ,then desire size 60mm if distance A is 70mm ,then prefer length 70mm Installation steps : Insert ball lock/Pay attention to the connection between the ball lock and the bolt/Install the baffle/Screw the cover/Align and insert the ball lock and set up it/check the ball cant be out /finish Soft note:1. Transition: 1 cm = 10 mm = 0.39 inches2. Depending at the gentle and the screen, the colour of the thing may be slightly varied from the colour of the picture.3. Allow 0.5-5mm distinction due to handbook measurement4.Material : Stainless metal 5. it match for the door thickness: 30-50mm6.if there may be huge order ,welcome to contact us free .TKS .