This a phenomenal little emergency pen. The build quality is rock solid--it's a little tube of stainless steel. The magnetic cap is plenty strong. I keep it on my key chain, and the pen has never once come loose or fallen off. The magnet is strong enough to give you a very satisfying snap when you insert or remove the pen. Inadvertently detaching the pen is quite unlikely. At under 3 inches long, it fits nicely in my key chain with my car keys. You can use any standard multi-pen refill. I use Fisher Space Pen U1F or U4F universal refills.