Vitamins add 10 EVs to the given stat. however they are limited 10 Vitamins per stat, or up to the first 100 EVs. you can have up to 255 EVs in any stat, but only a max of 63 points can factor in so 3 EVs would be wasted. usually the EV spreads are:
252/252/4, 252/180/36, or 252/160/88, but 508 is the maximum amount of total EVs.
Wings add 1 EV to the given stat, but are not limited like Vitamins, so if you had 252 Health Wings, that's 252 HP EVs right there. make sense?