Screen frame corners with locking slide latches in white plastic are designed to fit into 5/16" x 3/4" screen frame. The square-cut design allows for a non-mitered cut by the Do it Yourselfers. The latching design of the corner allows the screen frame to latch into the window frame.
From the Manufacturer:Screen frame corners in white plastic with black locking slide latches are designed to fit into 5/16" x 3/4" screen frame. Square-cut corners are designed to allow you the make square cuts instead of having to make miter cuts. The latching design of the corner allows the screen frame to latch into the window frame.