Cutting a tube coupler and centering ring shims, then gluing the shims onto the centering rings. The website for North Coast Rocketry, who makes a Kuhn Tube Cutter kit: http://northcoastrocketry.com/ The Kuhn Tube Cutter can be purchased either here: https://www.apogeerockets.com/Building_Supplies/Tools/Kuhn_Tube_Cutter Or here: http://www.erockets.biz/north-coast-rocketry-accessory-kuhn-tube-cutter-kit-800/ The BT-55 tube and the brown tube cutter were purchased from JohRocket: https://jonrocket.com/