World’s lightest pen? Perhaps. Anyway at @ 1 gram and for US$3 you have a 2 ½’ (6.5cm) pen which will write on practically any surface, even upside down or under water or in space.
Fisher Space Pen’s Sealed Pressurized Ink Cartridge: Performs in temperatures from -30ºF to +250ºF, underwater, in zero gravity, at any angle–even upside down! The ultimate in dependability! The choice of ski patrols, search and rescue teams, law enforcement agencies, armed forces, and everyone who demands reliability in a writing instrument.
The PR Cartridge is the fat one in the middle above. The U Cartridge is the skinny one on the top and bottom. When it arrives it will be long like the top image shows. It is made this way to fit several different pen barrels. If you need it to be shorter, just flex it back and forth at the break point and it will separate, leaving you the correct length.
Cartridge. Please note: the U Cartridges contain a much smaller amount of ink, they write about 1200 feet depending on your writing style, as compared to the regular PR Cartridge which should write more than 12,000 feet depending on style and surface.
POINT SIZES – Fine contains a .9mm Ball – Medium contains a 1.1mm Ball – Bold contains a 1.3mm Ball. Comes in 9 different colours. The ‘U’ refill costs about US$3: http://www.spacepen.com/cartridge.aspx Use with: http://www.theultralighthiker.com/waterproof-notepads/