Just don't want to screw this up...
Which is correct? A or B?
There’s no way of knowing
There may be a convention, but I see no reason why there SHOULD be a convention. You need the data sheet. The manufacturer’s (and therefore the ONLY) part number for a digikey 497-2753-5 is actually STPS1545D.
Here’s the data sheet. Look at the very first page. (There’s even a picture!)
Again, I see no reason why this should be the convention for ALL daiodes in TO-220 cases. But it MIGHT be.
If you’re still unsure, measure teh resistance with a multimeter. It will have infinite resistance one way and low resistance teh other way. That’ll tell you which direction it conducts.
huh?
What is a convention… and I couldn’t find it on the data sheet! Except fot the K and A on the pins… What is K and A?
Arrgg!! This is the last thing to solder! Just tell me which way it goes!!! 
Ah
Convention - just because a diode is in a TO-220 case doesn’t mean that internally there all wired the same! If they were, that would be “convention.”
OKay. K=Cathode (the negative end with the wiggly line on) A=anode (the positive end which is the end where the little arrowhead points AWAY from).
With respect to your pop quiz, B is the answer, but with respect to convention, I’m saying you shouldn’t assume this is the case for all diodes.
Dig it!
You da man, man!
DIY pedia
8ik
Race
If I’d known it was a race, I’d have produced a ray-traced short video of the answer. I can see it now. The part spinning on the screen, the plusitive and minusive ends glowing. Electrons whizzing on their merry way. Getting stopped by the wiggly line…
I could have been big. BIG, I tell you.
In the time it took…
In the time it took you guys to poke eachother… I GOT IT SOLDERED!!! DONE!!!
Now comes the blue smoke – I am so excited!
Dude, magic smoke is what
Dude, magic smoke is what it’s all about.
I like it better with caps, you even get confetti with it!
Smell
Actually, I love the smell of caps that have gone "phut."
do it on POV-ray and I’ll be
do it on POV-ray and I’ll be impressed.