1. Your broker has to support fractional shares.
2. Just add more decimal places:
0.1 is 10% or 10 shares.
0.01 is 1% or 1 share.
0.033 would be 33% of 1 share.
(check my math, is that right?)
As I understand Volume for placing a stock trade, Voulme is defined in what is called Lots and 1 Lot is equal to 100 shares.
If I wish to purchase only 50 shares of a stock, then I would specify 0.5 as my Lot which represents 50% or 50 shares in this case. And this is referred to as an Odd Lot...