One of these days I'll try a thread drive on The Classic...once I buy a VPS.
I don't think you can do thread drive without one of these.....the speed is gonna be a lot different using thread over o-ring rubber.
Maybe down the road..... 
John
I think you mean SDS? Because the thread is significantly thinner than a rubber belt it can cause a large speed change, so you need the SDS to adjust the speed.
Some people feel thread drive adds more "drive," more PRaT, since it is less flexible than rubber. I have found, however, that thread drive transmits more motor noise through the platter to the cartridge, even on a TNT with the motor isolated on a separate platform. And you can hear the knot "twanging" as it hits the motor pulley. YMMV.
John K.
