Here is a buck showing its scrotal attachment. This was scored as moderately tight. Anything looser than this I would not use. If it is very hot then the scrotal will loosen because this is part of the bucks cooling system. Be sure that both sides of the scrotal is even. You do not want daughters with lopsided udders.
Look for width in the escutcheon, a tight to moderately tight scrotal, level rump and a wide front end. A buck needs to have all over good conformation being level and smooth across the top and stand on good sound legs and feet.