No wait, the cap is 510 total. 252 is usually what gets put into a single stat x-x
"So, what are the limits? Well for starters, you can only gain 510 Effort Values before they will stop being counted. 510 can be called our "Overall Maximum", if you want a technical term. So this brings the Effort Points you can gain to 64, once again as a maximum. But this is still a bit much to add to any one stat, and it would make any Mewtwo have an absurd amount of Special Attack still, or Blissey still having that huge potential to go over 700 Hit Points (not like you still can't get there.) So, to make it limited still, there can only be a maximum of 255 Effort Points per stat, giving a pokemon a potential 32 point increase in any stat."
Moar