Originally Posted by 10is
TYPE-1 with the harder rubber are used for clay - I mis-stated the ball type in the previous email. TYPE-2 balls are the standard balls for hard courts and yes they remain unchanged. TYPE-3 balls (with a larger diameter) are what are used on grass.
Also, this article is from 2000 when they were still researching the use of a larger ball at Wimbledon which was consequently implemented after 2001:
Except that no players, commentators, nor authorities have ever mentioned that this experimental larger ball was ever ACTUALLY implemented in match play at Wimbledon.