Circle cutout is ID .725" and OD of .706" and is designed to use low-cost and easily available ½" EMT conduit which can be bought from your local hardware store.

The optional bottom plate uses #12 screws which allows you to secure the shelf to something for instance in a case like mine where I attached it to a slide out shelf in a cabinet. There's also an optional top plate for your top most shelf to give it a clean look.

You can use either the dowel style or pin style option. The dowel style has a looser fit and allows for easy removal whereas the pin style creates a more snug fit but once assembled cannot be removed.