Pen Bushing Size Calculator
Find the correct bushing outer diameter for any pen kit.
Match bushings to your pen hardware for a seamless finish.
Bushings are precision-machined metal sleeves that mount on the pen mandrel alongside your blank. They establish the target diameter — you turn the blank down until it is flush with the bushing surface.
Why Bushings Matter
Each pen kit has specific hardware components (center band, cap, nib coupler) with fixed outer diameters. The bushing OD matches these hardware diameters exactly. If you turn past the bushing, the blank will be too thin and leave a visible step at the hardware joint.
Standard Bushing Dimensions by Kit
| Kit Style | Upper Bushing OD (mm) | Lower Bushing OD (mm) | Center Bushing OD (mm) | Mandrel Bore (mm) |
|---|---|---|---|---|
| Slimline 7mm | 10.4 | 9.8 | — | 7.0 |
| Fancy / Euro | 12.4 | 11.8 | — | 8.0 |
| Cigar | 14.8 | 14.0 | 15.2 | 10.5 |
| Sierra | 14.2 | 13.6 | 14.8 | 10.0 |
| Bolt Action | 14.0 | 13.4 | — | 10.0 |
| Wall Street | 16.0 | 15.2 | 16.5 | 12.5 |
| Majestic | 17.0 | 16.2 | 17.5 | 12.0 |
| Rollerball | 14.0 | 13.2 | — | 10.0 |
Understanding Upper vs. Lower Bushings
The “upper” bushing sits at the cap end of the pen (typically slightly larger because cap hardware is wider). The “lower” bushing sits at the nib end. Some kits (Cigar, Sierra, Majestic) have a center bushing for the center band.
Wall Thickness at Bushing Diameter
Wall thickness = (Bushing OD - Tube OD) / 2
For a Slimline: (10.4 - 7.0) / 2 = 1.7 mm of wood wall. This is quite thin, so work carefully at low speed as you approach final diameter.
For a Cigar: (14.8 - 10.5) / 2 = 2.15 mm — slightly more forgiving but still requires gentle final passes.
Worked Example — Sierra Kit
Upper bushing = 14.2 mm, lower bushing = 13.6 mm, center bushing = 14.8 mm. Tube OD = 10.0 mm. Upper wall = (14.2 - 10.0) / 2 = 2.1 mm. Lower wall = (13.6 - 10.0) / 2 = 1.8 mm.
Turn each barrel section to match its adjacent bushing. Frequently stop the lathe and check by feel that the blank surface is perfectly flush with the bushing edge.
Custom Bushing Tip
If you cannot find commercial bushings for an unusual kit, measure the hardware components with digital calipers and turn your own bushings from aluminum rod on the lathe. Bore the center hole to match your mandrel shaft diameter.