This Yoke is designed to work the 21mm Large Chuck for our SVS II Deluxe Refacer. It is meant for customers who are changing from a Standard Sized Chuck to our Large 21mm Chuck. You will also have to perform minor grinding of the Chuck Cover so that it will fit over the larger Chuck Assembly.
If you have questions or concerns over this procedure you can call our Technical Support at 1-800-553-5953.