hay guy we have been using a transfer block i make. it can take small and large stones. i sell for what it costs me to make plus shipping. the gap is 78 mm and bow at center is 38 mm or compfortable a 65mm diameter stone with use with any dops 2″ or longer, diameter 5/16″ and smaller. we’ve been using them with all our machines, o’brien, mdr, ultra tec, raytech, Lees, etc. i sell for $20 to get my money back, if bigger gap is needed it can be done not much diff in cost. made in one piece so slot is straight in line. with screw down lock downs. email me for pictures gemmakemz@cs.com