The stab is just shy of 11/16" thick at the center or about 17mm. Any servo more than about 1/2" thick may not lie flat in there without bulging. The ribs have oval slots in them so you can get a servo lead through there. As opposed to what I said before, you will not have to cut the ply mount in the stab, but you will still have to drill a hole in the top of one of the fins.