Modular Fountain Pen (JOWO #6) Compatible

A fully 3D-printed fountain pen body designed to pair with widely available JOWO #6 nib units and Standard International converters. No proprietary parts, no expensive kits — just print, screw your nib unit, drop in a converter, ink up, and write.

Why this exists

Good fountain pens are expensive. Good customizable fountain pens don't exist. This design gives you a functional, comfortable writer you can print in any color or material your printer handles — and swap nibs or converters whenever you want.

Compatibility

• Nib unit: JOWO #6 (press-fit). Also tested with Bock #5 housing — fits with light friction.
• Converter: Standard International (Schmidt K5, Monteverde, or any SI-compatible converter)
• Also accepts Standard International short and long cartridges

Print settings (tested on Bambu Lab X1C / P1S)

• Material: PLA or PETG recommended. PETG for better ink resistance.
• Layer height: 0.12mm recommended for smooth barrel feel and tight tolerances
• Infill: 20% gyroid
• Supports: None needed
• Orientation: Print barrel upright, cap upright, grip section upright
• Post-processing: Light sanding on the inner grip bore with 400-grit gives a perfect nib unit fit. No glue needed.

What's in the files

• Barrel (standard length)
• Screw-on cap with inner cap sleeve
• Grip section (JOWO #6 fit)

Assembly

Takes about 2 minutes. Screw the nib unit into the grip section, thread the grip onto the barrel, insert converter from the back, cap it. Done. 

What's coming next

This is the first design in a modular fountain pen system I'm building. Coming soon:

→ Pocket-size barrel variant 

→ Oversize/cigar-shaped barrel 

→ Kaweco Sport nib unit grip section 

→ Magnetic cap option 

→ Multicolor AMS-optimized editions 

→ Clip variants (standard, roll-stop, deep carry)

Follow me if you want to see the full system develop — I'm designing toward a complete "build your own pen" ecosystem where you mix and match barrels, grips, caps, and clips for any nib unit you own.

Feedback on fit, tolerances, and what nib units you'd like supported next is very welcome in the comments. This project gets better with your input.

Non-printed parts you'll need

• 1x JOWO #6 nib unit (~$8-12 on Amazon/Goulet Pens/AliExpress)
• 1x Standard International converter (~$3-5)
• Ink of your choice

License: Personal use. Commercial license coming soon for makers who want to sell printed pens.