I thought single strength glass was the term used for 3/32 inch glass, like in picture frame and such. Double strength would be 1/8 inch glass like in a lot of windows and plate glass was thicker glass of varying thicknesses. It's all terminology I guess.
1/4 inch glass should be fine for 13 inches of height, bracing would be a good idea as I'm not sure how much bowing you'd get on a 3 foot span.