We also call these springs a "reverse C" Type spring because the one end bends back in towards the center of the spring in what looks like a backwards C. The drawing illustrates the measurements needed.
Example: Part Number C-4 would measure 13 11/16 x 14 1/2 along the flat length (a, b) and these springs are .360 x 1 3/4 material. The free length "c" is approximately 26 1/4". These springs are rated for 1750 lbs per spring and are usually used on boat trailers. There are 4 leaves in total