Shown: the base of the larger sculpture showing the 11 to represent the year 2011.
Notice the 1 to represent the year 2001 in the previous photo. These bore holes were part of the original block that was sculpted, made by huge equipment as they were cut out of the original slurry wall of the WTC. There are no accidents in art, San always says. She took what some might of viewed as an imperfection in the stone and made it part of the sculptures design instead.