public class TestNum : NumericUpDown
{
protected override void ValidateEditText()
{
if (base.UserEdit)
{
base.ValidateEditText();
}
}

protected override void UpdateEditText()
{
Text = Convert.ToInt32(base.Value).ToString("00");
}
}

this.numTest = new System.Windows.Forms.NumericUpDown();
private System.Windows.Forms.NumericUpDown numTest;

this.numTest = new SampleForm.TestNum();
private TestNum numTest;

public class HexNumericUpDown : System.Windows.Forms.NumericUpDown
{
    public HexNumericUpDown()
    {
        Hexadecimal = true;
    }

    protected override void ValidateEditText()
    {
        if (base.UserEdit)
        {
            base.ValidateEditText();
        }
    }

    protected override void UpdateEditText()
    {
        Text = System.Convert.ToInt64(base.Value).ToString("X" + HexLength);
    }

    [System.ComponentModel.DefaultValue(4)]
    public int HexLength
    {
        get { return m_nHexLength; }
        set { m_nHexLength = value; }
    }

    public new System.Int64 Value
    {
        get { return System.Convert.ToInt64(base.Value); }
        set { base.Value = System.Convert.ToDecimal(value); }
    }

    private int m_nHexLength = 4;
}