• SEALED PRESSURIZED INK REFILL • Refill tip is Ultra-hard Tungsten Carbide Ball, Stainless steel precision socket prevents leaking yet delivers uniform ink flow. • Writes underwater, upside down, at any angle,extreme temperatures from – 30º F (-35º C) to +250º F (121º C), over grease, 3 times longer than the average pen, etc. • Compartible with all standard Fisher cartridges. • Come with branded Clip. • Cap slides over the barrel to activate mechanism. • Made in the USA. • Fisher M4B Lacquered Brass Cap-O-Matic Space Pen. • The pen's metal and it has a solid spring driving the cap-o-matic click top which is the only moving part. • The ink is smooth and doesn't smear. • It'll write on the inside of a butter wrapper, underwater, upside down, extreme temperatures and just about anywhere. • The refills are really cool and functional. • Charged with Nitrogen filled Thixotrophic ink, providing a steady, smooth stream of ink regardless of gravity or grease. • Just touch the pen to your writing surface and the ink flows. • Best of all, there are no loose parts inside the barrel, so you don't have to be careful of things like tiny springs when you're changing the refill and this is a definite plus point.