Traffic Sign Materials. Post and fixings:- Plastic coated, hollow steel posts and 76mm clips to securely mount your Reflective Traffic Safety Signs. • Available in three lengths, we recommend the use of a baseplate and to allow approximately 600mm sink below the ground. • Plastic end caps are available for the tops of posts. • The screw band fixing and universal channel clamp will allow fixing to existing posts up to 160mm in diameter.