I'd take a good look at where it is in the circuit, for example if it's
across the power input on automotive equipment it would be safe to
assume it's an 18 volt Zener, or a VDR.

If it's a rectifier and has fat leads it might be a high current (18
amps continuous) diode, plain and simple.

Hint : Look at the circuit if you can see it, that tells you what the
part is. Up until about the last decade I've prided myself on working
on electronics without a print. Sometimes you have to think "What would
I put there ?". Or even, well, what does it need there ?

Even now, like horizontal ouputs, they ask me when we don't have the
exact one in stock. I see the original and usually get the specs on it
from datasheetarchive, but when I can't get the data I can still make a
good guess by looking at what it's in.

If it's a bigscreen and had a 2SD1556, it can take a 2SC5150, although
they cost a bit more. If it's a 13", gotta look at the driver
transformer, the smaller it is the higher gain you'll need usually.

Trouble comes when you get to Zeners, but usually there is a filter cap
across it, look at it's voltage rating ! Yes, it can be done, but it is
harder and harder these days.

As much as I hate to do it, I suggest you restart the thread because
I'm missing alot of replies because there is so much traffic. soon,
I'll try to correct this with a new newsreader, but for now you should
give us some details about the equipment your mystery diode is used in.
Also, throw the first or last part of those numbers, incompletely and
severally in the search engine at datasheetarchive.com or
alldatasheet.com

You might find a series of diodes that match the general description
and be able to call it a day.

JURB