A 0.1" pitch 2 start screw is the same "resolution" as a 0.2" pitch 1 start screw, that is both are 5 turns per inch. For a single start screw turns per inch and threads per inch are the same, but for multi-start screws turns per inch is equal to threads per inch divided by the number of starts.
So if you had a 10 tpi single thread screw and wanted to increase the speed of your machine (assuming that you had enough power), you could replace that screw with either a 10 tpi 2 start or a 5 tpi single start to effectively increase the speed at which your machine could travel (again assuming that you have enough power). This is because the new screw moves something along the screw twice as far with each turn.
The trade off is resolution versus speed. For the same number of steps per rotation of the screw, going to a screw that moves something twice the distance with the same number of turns, means that it moves that thing (whatever it is) twice as far for each step (less resolution).
Alan
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