NumberFormatInfo

The initial settings for a NumberFormatInfo or DateTimeFormatInfo are based on the invariant culture.

The following code creates a NumberFormatInfo and change the group separator from a comma to a space, then use it to format a number to three decimal places:

using System;
using System.Text;
using System.Globalization;
class Sample
{
    public static void Main()
    {
        NumberFormatInfo f = new NumberFormatInfo();
        f.NumberGroupSeparator = " ";
        Console.WriteLine(12345.6789.ToString("N3", f));

    }
}

The output:

12 345.679