I've been using the Great Planes nylon cone with aluminum back plate for a few years now on my four strokes from 45 to 91. Not a hint of slipage with them. Like a couple of the guys said though the plastic back plates just will not hold up the the tightening required on the Four strokes.

Here is the ones' I'm talking about'
http://www3.towerhobbies.com/cgi-bin...?&I=LXBMY1&P=7

Don