The original vinyl window screen corners degraded with UV and heat so I designed replacements.

This corner pull tab is designed from the original but with a thicker handle section to avoid UV degraded breakage.  

The thinner section at the midpoint is designed to align with the profiles of the screen's frame (for the spline), to fit within the recess of the window's frame and to enable the tab to flex outwards slightly to get a finger (or thumb) between this pull-tab and the taught window screen. 

Spline roller recommended to replace the screen's spline.