These are my favorite Whites strains with there unique square design. Some of these are marked with the Patented May 27, 1913 date or just Patented. The patent was USD44118S and showed for the square design and the cylindrical design. Perhaps this was for the ones marked Patent Pending. These have teat rests and some are marked with the Square D Co. logo. I have yet to aquire a number 502 but will keep looking.