The back plate is 2" x 6", has a "part number" of "1140-3" embossed on its rear side as well as a "U.S. Pat. Pend.", but no manufacturer data.
The piece that failed is the plastic cog in Image #3, which holds the knob onto the back plate.
The latch is approximately 20 years old.
![User submitted photos of a storm door handle.](/images/pictures/2014/06/36322.jpg)