Rootstock ONLY is just what is says; "rootstock only."  There is no grape variety grafted to it.  Use this option if you want to do your own grafting in the field. This is a great option for shade arbors also.  Rootstock varieties produce little or no fruit.  But, they look just like a fruiting variety without the maintenance and care that comes with producing fruit. Rootstock varieties are also Pierece's disease resistant.