Cap-O-Matic Space Pens All metal, .383" diameter cap. Contains a #SPR4 Black Ink, Fine Point Pressurized Fisher Refill. Fisher Space Pens write in temperatures from -50º to 250ºF, underwater, in zero gravity, at any angle–even upside down! That"s why they"re the choice of ski patrols, search and rescue teams, law enforcement agencies, armed forces, and anyone who demands writing reliability in adverse conditions