@shaiko : I do not require very high speed, 100 RPM would do fine. It needs to turn a little socket with no load. The socket is cylindrical shaped and weight less than 50 grams or less.
@SunnySkyguy : There is no lock. I know lock is required to stop it instantly, but thats not the problem if it get like 5 more turns because of speed force or whatever it is called.
I do not know much about power to be in specific words. But lets just say, it should have enough power to get the plastic socket sanded with very little human finger force. Like, you put tiny sandpaper in between index finger and thumb and you put very little force just to get feeling it is getting sanded. Yes it sound crazy, why need specific turns for sanding, but its just for showing how much power is needed.
Accuracy is not important in this case. Also, as far as I know servos are bound to specific angles, they have limits, they cant turn 0 to 360 degree and continue but I could be wrong.
@Warpspeed : Stepper motor is very good but they cost more for this project.