Probably a dumb question but looking at replacement shift and brake cables, I see Shimano offers an Ultregra set, Dura-Ace set, etc, and also a universal set.

What is the difference? Is it just a quality level or something related to how they fit to the different components?

Quality levels and FEATURE levels.... the "Fit" is up to the installers....

and it's not just the cables, the CASINGS are usually different, too.

All cables are not created equal. But I've never come across any that are specific to a groupset. Campy have slightly smaller anchor "buttons". Road and MTB (well, flat bar...) brakes use different anchor buttons. I seem to remember some DT shifters with a different shape/orientation than the others. Like a flat bar brake but smaller.
Brake cables are different from shifter cables.
The rest is optional.
Die-drawn?
Teflon-coated?
Stainless?
Galvanized?
They all have their pros and cons, and the difference is rarely critical.

The difference is in the materials used to make them. The upper levels probably use stainless cables over galvanized ones, and the probably use nicer housings as well.

However, with that said, I always use the cheap ones because regardless of how nice they are, water still gets in there and I generally replace them every year anyway.

Google shows ultegra and Dura ace both show OT-SP41 and polymer coated (inner) I suspect the outer isn't anything different than the standard shimano SIS-SP41 lined outer.

Campy shift cables have slightly smaller heads than Shimano's and using Shimano size cables in Campy brifters can lead to a nasty jam that very difficult to remove in the future. Other than that and within a given brand, the cables are interchangeable.

BTW, if you do get a Shimano or Jagwire teflon coated cables, be sure to scrape away the coating where the derailleur pinch bolt goes. Otherwise I promise you it will slip and the shifting will get unreliable until you clean it off and reclamp.

Thanks for all the replies and information....especially about scraping off the coating at the pinch bolt. Just the thing that I would not have thought to do.

Doesn't Dura Ace need electrical cables? I recommend the ones that are made of pure silver with gold contacts, they should shift better.

Really? Isn't that an overkill? Both my 1990 Schwinn Miranda (man and woman version) still have their original cables and they are still working well.

Monster brand?

No, but Dura-Ace and Ultegra Di2 do.

So long as the signal gets successfully transmitted to the derailleur, it'll shift exactly the same regardless of whether the wire is silver or copper. Not that you have a choice anyway, since Shimano doesn't sell Di2 e-tube wires in different configurations; just different lengths.

(Some people claim to hear a difference between silver and copper wire on analog circuits like speakers. I don't buy it. Neither does my oscilloscope. And it makes literally zero difference in a digital circuit where the signal is binary. Ones and zeroes are ones and zeroes, regardless of the transmission medium.)

What will happen if you leave a bike outside under rain for a week?
Will the cheap Shimano wire oxidize and fail?

I think (hope) Barabaika really knows that only DI2 groups use electric wires and that he was also kidding about the silver and gold wire sets. At least I'll give him credit for being facetious until he proves otherwise.

That said, there is a significant market for absurdly priced "premium" connector and speaker wires for sound systems among the naive. P.T. Barnum's 1st law is alive and well; "There is a sucker born every minute."

In 10 years even Tiagra will be 13-speed DI7. There will be a huge market for nice cables.

Sometimes, irony still gets delivered without accompanying smiling faces which makes it hard to detect.

As for the Audio stuff, i'm puzzled. I myself am an engineer by trade and kid myself to be not easily bull****ted in matters techncal, and for a long time i was among those who believed those expensive speaker cables were sucker baits.
Then a friend of mine who is a hardcore audiophile told me he *could* identify the difference in quality between an already not-so-cheap set of speaker cables and a very good one both in a blindtest at the shop and at home with his own set, so he bought them (and being a social worker, he has no money to throw away). I know him as a very rational guy. So i'm really looking forward to the test he offered me as a sceptic - haven't got around to it yet.

And completely unnecessary.

I use Jagwire Road Pro, teflon coated cables, no slippage issues.

Then your results are different from mine. I neglected to remove the coating from the first cable of this type I had and shifting began to slip after a couple of rides. I readjusted it, tightened the clamp bolt even tighter, and the same thing happened. Finally, I scrapped off the coating and the shifting has remained stable ever since. And, yes, I do know how to tighten the clamp bolts and have never had any problems with any other type of cable or these after removing the coating under the bolt.

Yes, old bikes can use their cables for longer because the indexing (if present) is much less picky.

Try using a 20 year old cable and housing on a modern 9 or 10 speed and you'd see much different results. Cables and housings are cheap. Once a year IS probably a bit overkill, but it's ~$15 a year to make sure my shifting is dead on and not have to touch it for the rest of the year.

Thanks. That does make sense. My current bike is 5 years old. I can see the rear brake cable was already changed. My derailleurs still shifts flawlessly (once I adjusted them). I'll keep that in mind for my next Spring tuneup or if the shifting becomes problematic.

Cables actually stretch after they are installed, and you have to tweak the derailleur settings for a couple weeks afterwards.

Google "how to pre stretch derailleur cables"

I personally don't do it, cause I know how to use a barrel adjuster and can adjust while I'm riding.