lol a capped 18ml pen is a home defense system. there may be one or 2 with optional caps pop out of the shop but it's going to be so insanely huge. Larger than a Waterman #20 in fact.
the 18ml reservoir is 6" by itself. with the barrel, section and nib in place we are at 8 1/2-9"" uncapped. with a cap, another 1 1/2"- 2 inches minimum. so 10-11" capped. Posted..I cant even think that big...lol
OD of the barrel will have to be 13/16"-7/8" at the smallest.
Thats like one of those souvenir kiddy/baby sized baseball bats you win at the state fair or get at the ball game.
__________________
Tu ne cede malis sed contra audentior ito ~Yield not to misfortunes, but advance all the more boldly against them