What you are saying doesn't add up. Yes, it is very likely a diode with the black stripe identifying the cathode end. However, if you know the specs then you can just get a diode that matches them. If you don't know the specs, then how do you know you want another one?
You say it "works", but how do you really know except for whatever conditions you have tested it with? Show the schematic it is in and give particularls like voltage of power supplies, expected currents, etc, and we can probably recommend a diode that will do.
For example, for basic hobby rectifier use for 50V or less, the very common and cheap 1N4001 will do fine. Same thing for up to 400V is 1N4004. However, your diode may be a zener, which makes things different. You could even be using it as a rectifier and not know of its zener characteristics.
All in all I would forget about this diode. If you don't know what you have, you basically don't have anything. Figure out the specs for what you really need and get a diode based on those.