no, the other side. the stem that is on the inside of the key.
most folks seem to cut them out of cheap keycaps to reuse them, but at least some custom key caps have a little plastic stem glued onto the back of an otherwise hollow key. -- as if the stem had been cut off and replaced.
in the case of wooden keycaps, this makes sense, as wood will be pretty brittle across the grain in the small cruciform void of the MX stem.