This is a support piece that screws into the door frame that provides support for heavy and/or sagging screen doors. I recently installed a screen door an noticed after time and weather it started sagging.

There are 2 countersink #8 screws that allow you to mount to the door frame. There is also a gentle slope at the top of this piece that guides the screen door into position. Pretty specific piece, but I figure I might as well post it.