I would like to install an extension in one of my older shafts so I can use it in my driver. Its an older UST Mamiya Helium, R flex, 46 grams. I measured the outside butt diameter at 0.613″ and the inside diameter at 0.562″. I’m a little confused with the color coding for the premium extensions indicated in the Golf Works catalogue, so I’m not sure which one to order. When I do order one, I’ll also order the extension gauge. Just to clarify for me, the O.D. dimension noted in the catalogue for each extension, is it the O.D. of the extension that fits inside the shaft or the outside shaft butt diameter?