0.38mm pen refill?

[medlongpens]

I just had someone ask me to make the a pen with a 0.38 pen refill in it, just like the pilot g2 gel pen. Does anyone know of a pen kit or refill that would work?

 

[ChrisN]

Pilot G2 refills fit in rollerball pens, but rollerball pens are capped, which they may not want.

 

[medlongpens]

Thanks for the help.