| on most dbs a player can get up to the F# on the g string without entering thumb position. it is a matter of feeling and choice how these notes (D-F#) are fingered. some say that once you have your hand in the crook of the neck that the 3rd finger should be used - others not, whatever.
thumb position can however be used any place on the bass, but as you know it is most common on and above the G harmonic (cutting the g string in half). i will not try to explain the technique because it is something that i am still devoting alot of practice time to... but two important points are:
1. (and this goes for about everything you do on db) use your arm weight, gravity, and try to feel as though your body is applying your left arm as a lever against the bass. don't just push with any one part. your body and the earth as a whole play the bass.
2. try to find a comfortable position where you are not depending on the surface of the bass to support your arm. you should try to maintain complete freedom of motion - that the transition between thumb position and "regular" position is smooth, and that you have complete access to the finger board.
i would suggest thinking of the harmonics as nodes for the thumb and begin from there when working out fingerings. and good luck with that callous. that part is really no fun to start with.
peace
charles | 
I'm now frealy learned to play all to D on G string but after that... Please some give me tutorial or link to how to play with thumb on double bass! I need to know it a little bit untill this fridey. PLEASE HELP SOME TUTORIAL!!!!!!
