Temp gauge lens retainer used on the inside of the cluster bezel to shield the face of the gauge. Will show a minor amount of wear or rust, plan on cleaning it up and possibly repainting. There are 3 total retainers needed per bezel, 1 of this style and 2 for the amp and fuel gauges (they are notched for different placements). Ford called these retainers a 'mask'.
Ford part number C7WY-10890-
NOTE: The temp gauge retainer is painted all black, the amp / fuel gauge retainers have a white painted face.