Carbide Insert Trimming System.A perfect pen requires perfectly fitting parts, and barrel trimming is THE essential process to make square barrels. This new barrel trimming system makes this process a snap with its ultra-sharp carbide cutters to trim faster, cleaner and easier than ever before.The cutters cut a pristine smooth surface for mounting your pen parts, they also rotate so you never need sharpening while eliminating burrs in the brass tube interior. Cut precise square barrels made from wood, acrylics, polyesters, ultra-hard and natural materials.System includes 2 interchangeable carbide cutters a pilot shaft and 5 pilot sleeves. The 7mm tube pilot shaft and 5 insert sleeves provide the ability to trim an additional 8 tube diameters (7mm, 8mm 3/8in., 10mm 25/64in., 10.5mm, 27/64in., 12.5mm and 31/64in.).Large cutting surface trims barrels that are over 1in. in diameter.