This Droll Yankee Seed Tray with fit the A-6 Ring Pull feeder, both the thistle or sunflower feeder.  It will also fit the Droll Yankee yellow thistle feeder.

A simple plug screws it into to bottom of the feeder.  Lots of drainage.  It is 7.5 inches.

On a sunflower feeder this will give cardinals a place to land.