In addition to SA's answer, you can use
InvariantCulture
:
double a = 0.125;
string txt = a.ToString(System.Globalization.CultureInfo.InvariantCulture);
double a2 = double.Parse(txt, System.Globalization.CultureInfo.InvariantCulture);
I prefer this solution to store standard formated data into a file. You don't need to bother wich culture you used once you want to load them.