I bought 2 a year or so ago and they are different . One twists at the finial end and the other twists at the nib end like a regular sierra. The one I just finished today appears to use a standard Sierra tube and I used my Sierra bushings. The outside diameter of the one I did today is just slightly more than the Sierra so I just turned it a bit large and used my micrometer to sand the last little bit to final dimensions. The outside diameter of the one that twists at the finial end is just a little larger again but I think I used my Sierra bushings for it as well.