The Monarch style registers are either made of cast bronze or cast aluminum. The bronze castings are available in three different patinas, as well as nickel plating. The aluminum castings can be had in three painted finishes.
Choose with with dampers (14 inch sizes or less), with screens, or neither. If you get neither then the unit is completely flat on the back, which can be useful if you have a non-standard duct opening that is difficult to work with. Flanges on Monarchs are typically about one inch, although can run as much as 1 1/8 inch.