Nope. It doesn't work. I tried that exact method and the knob came off after 2 days (ANNOYING). I had the exact same problem as milford is having with MY autotechnica gear knob.
It really depends what type of gear knob you've bought. There's the cheaper type with a main body and a kind of alloy "hand plate" where your palm would go mostly:

or the more expensive type with a metal/wooden body which feels a lot more solid (I have used both types - the former broke after one day)

The cheaper version has a plastic fork design built into the top of it. Don't even bother using those rubber fittings, no matter which knob you've bought. None of them fit properly on the u12 gear stick. The cheap version will
screw straight on to your gear stick by cutting a thread into the "forks" at the top. Try it, it works.
The more expensive knob is a little more difficult. To get it to fit properly, you'll need to redrill the hole at the top and, for best results, tap a thread into it with the correct pitch/diameter (I think it's 10x1.25) - you can pick up a tap&die set at any hardware shop for about $25 if you don't have access to one. NB: This also makes the knob sit lower, which is better.
After this, tighten up the little screws at the bottom, and it should be fine forever after. If you don't want to go to all this work though, I'm sure there must be a better way of doing it. Good luck champ
