Public Class PartNumberTypeConverter
        Inherits System.ComponentModel.TypeConverter
 
        Public Overrides Function CanConvertFrom(ByVal context As _
          System.ComponentModel.ITypeDescriptorContext, ByVal sourceType As _
          System.Type) As Boolean
            Return sourceType Is GetType(String)
        End Function
 
        Public Overrides Function CanConvertTo(ByVal context As _
          System.ComponentModel.ITypeDescriptorContext, ByVal destinationType _
          As System.Type) As Boolean
            Return destinationType Is GetType(String)
        End Function
 
        Public Overrides Function ConvertFrom(ByVal context As _
          System.ComponentModel.ITypeDescriptorContext, ByVal culture As _
          System.Globalization.CultureInfo, ByVal value As Object) As Object
            Return New PartNumber(CStr(value))
        End Function
 
        Public Overrides Function ConvertTo(ByVal context As _
          System.ComponentModel.ITypeDescriptorContext, ByVal culture As _
          System.Globalization.CultureInfo, ByVal value As Object, ByVal _
          destinationType As System.Type) As Object
            Return CType(value, PartNumber).ToString
        End Function
    End Class
 
    <System.ComponentModel.TypeConverter(GetType(PartNumberTypeConverter))> _
    Public Class PartNumber
        ' ....
    End Class

 Public Shared Function Parse(value As String) As PartNumber

Those people who think they know everything are a great annoyance to those of us who do - Isaac Asimov