Bushings are small pieces of metal used to align and size pen blank tubes on a mandrel. Additionally, they can be home made of corian or acrylic. The quality of a bushing depends upon the accuracy of the machining used to create the bushing. Because the fit of the pen tube to the fittings is critical to a quality pen, always use a caliper to finish the pen blanks to the exact size of the fittings.
These are standard pen mandrel bushings. They mount on a standard pen mandrel. On the left is a standard 7 mm bushing intended for Slimline and similar pens. In the center is a set of bushings intended for a pen that only has a single tube. On the right is a set of three bushings for a standard pen having two barrels. Some bushing sets have three or four pieces depending upon how they are made and purchased as a set.
This is a turning between centers bushing. It differs from the previous bushings in that there is no hole in the center. Instead there is a 60° recess in the bushing. Only one barrel at a time may be turned using these between centers bushings.
This photo shows the 60° recess in the end of the bushing