10.7mm / 12.2mm drill bits are required. Double line center ring and threaded 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.