Regexp in C#

Regexp

using System;
using System.Windows.Forms;
using System.Text.RegularExpressions;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void OnlyNumbers(TextBox txt)
        {
            txt.Text = Regex.Replace(txt.Text, @"[^\d]", "");
            //txt.Select(txt.Text.Length, 0);
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            TextBox text = sender as TextBox;
            OnlyNumbers(text);
        }
    }
}