These brackets are designed to allow you to fit a pole in a recess. This drop-in bracket is for use where you are using two recess brackets.
The additional image shows the bracket in use with a 20mm pole and a Disc finial (secured a few cm from the end of the pole to act as a ring stop). This bracket is available to fit either 16mm or 20mm wrought iron poles or 25mm wood poles.
The screw that is fixed within the cup is always a countersunk screw. The other screw is either a coach screw or countersunk screw.