simpler than you think...............you can buy them for cheap right here...

http://www2.towerhobbies.com/cgi-bin...?&I=LXHY63&P=0

as MinnFlyer explained, they have an O-ring in them which is why i bought a few of them for back up.
i have a High Point balancer and couldn't find one of these to replace the one that wore out, and the TF cones work perfect.
i also like the TF balancer.........easy to setup and i don't have to be so careful in regards to dinging up the balancer wheels as i do on the High Point.