The rubber strap has to be cut to fit. Use a good pair if scissors and work your way down to the proper size. Once you cut it you can't go back. Theres a fine adjustment inside the clasp that lets you move it about a half an inch or so. It's a really nice set up, and the clasp, its hard to believe it's a rep!
I've got seven inch wrists and Im on the second to the last set of holes in the strap, so it could be adjusted down even smaller.