Set NumberGroupSeparator : NumberFormatInfo : Development Class C# Source Code

    

using System.Globalization;
using System;
public class MainClass {
    public static void Main() {

        NumberFormatInfo f = new NumberFormatInfo();
        f.NumberGroupSeparator = " ";
        Console.WriteLine(12345.6789.ToString("N3", f));   // 12 345.679
    }
}