10 mm drill bit is required. American style center band and twist pen cap.
Note: Since both tube are closed in one end, please spare the blank 3-5cm longer as to turn the end round. Mount only one bushing to mandrel and push the barrel end tight by the tailstock live center. To keep the barrels turning in center, make your own wooden bushing to fill the space between tubes and mandrel.
The short barrel should be turned about 4mm long (to the original brass tube) to press the center band.