Brass Shell Door Knocker - Nickel Finish Complete With Fixing Screws  . The door knocker is attached by 2 screws that  are approximately 40mm apart on the back plate. Screws included.  .   Easy to attach, with screw bolts which are provided. . Approximate Dimensions brass Shell: Width – 10.5cm  Height – 9.5cm  Screw holes distance - 4.3cm . How to care for your Shell door knocker  Your door knocker should just be washed with warm soapy water. Always avoid using abrasive materials which could scratch the surface