The cymbals in a pair of hats are different weights. The heavy one is usually on the bottom.

Interestingly enough, nudrum isn't neccessarily right on this one. BOth of the Z Custom DYno-Beat H-Hat cymbals - both top and bottom - are "EXTRA HEAVY," according to Zildjian.

Now, does that mean they're the exact same cymbal? Not neccessarily. The hammering seems to be the same, but it might be slightly different. Or they may lathe it differently. Or there might even be a significant weight difference between the two, just not enough of one to warrant a difference in the weight category that they are currently under.

COnclusion: I don't know, but don't assume anything. I'd go to a guitar center and play the top and bottom separately, and see if they sound like the same cymbal.

Or, you could just go for it and by the two tops or two bottoms. Lots of drummers do that - I"m sure it'll sound okay.

Or, you could just skip the hassle and pony up the $23!

Well I wasn't necesarily saying they would be classified as different weights but that the cymbals that are sold in a set usually have different weights. But I am working without research so not only will YMMV but IMBW (I Might Be Wrong)