jst2878: I got 18mm hole stops for the larger holes, and 16mm hole stops for the center holes. I am getting them from
www.conrad.com...... but the problem is they won't ship to North America. I also have an assortment of 11/16, 5/8, and 9/16, which I understand work ( as per imola4.8 ). I am gonna try the 18mm and 16mm first, when they get here. You need to find someone across the pond to get the goods from conrad.com and then mail them to you.......