The Tower starter comes with a rubber insert. If the big open end is too big to grab your spinner, or spinner nut, you can install it backwards and use the 'flat' end. I bought a replacement insert for mine that's designed for small spinners and spinner nuts.

http://www2.towerhobbies.com/cgi-bin...?&I=LXBC75&P=6

The photo doesn't show it, but one end has a hole that tapers from 3/4" to 1/2" and it works great on spinner nuts, acorn nuts, and small spinners.