Mays hit his 500th in 1965 while Robinson hit his in 1971. Back in the day when hitting 500 home runs was a commodity for a select few both Mays and Robinson were tops in their class.
September 13th certainly does mark a special day in baseball lore.
Willie Mays Topps 1970, # 600: the eyes awaiting a home run pitch (I know it is a photo from spring training but I still love those intense "eyes")
Frank Robinson Topps 1967 #100: another shot of the "home run" eyes Ranking 4th (Mays with 660) and 7th (Robinson with 586) in career round trippers, I salute Mays and Robinson for reaching that 500 HR club on the same day, albeit six years apart.
It was twenty one years ago that Sheffield appeared in a major league uniform, with a gold chain, silver braces and a label of a "future star". Since then he has been mired in controversy and played in an era (steroids) that will be forever tainted. However, he has reached this "milestone" and should be given his due (for at least one day).
I also like the back of this 1964 card of Banks for this reason; he just completed his tenth full year in the majors and the stats are easy to calculate his career year-to-year averages (just divide by ten or drop the last number, you can do the math): 1500 games, 1617 hits, 250 doubles, 353 HR' and 1026 RBI's. Not too bad for the first ten years of his career.