i use un-308L-16 can get at tractor sup.
northern tools and ace hardware

 

Why don't you just go to a real welding store???

By the way be careful what you buy through Northern Tool.
They leave out a lot of important info on automatic welding helmets,
and many items are not described properly and are actually UNSAFE.
I have called them and told them so, and they always say "We are taking that off of the list"
Of coarse by then many customers already bought inferior things.

 

It's all dependent upon which grade of stainless you're welding.

 

meathead,

As Supe said, it depends on what alloy of stainless you are trying to weld.

For 'standard' 304 grade stainless, 308 filler is used.

More info? Try this document as a start http://content.lincolnelectric.com/pdfs/products/literature/c610.pdf

There are other documents too. Like this one http://content.lincolnelectric.com/pdfs/products/literature/c64000.pdf

 

90% of stainless in the world is 300 series. among the 300 series 308 will work favourably with nearly all the grades and stainless to mild steel welding.

308L is the go to rod unless you know 100% your corrosion conditions that cause you to use something better than 308

 

You didn't pay attention to what rod you were welding with? WOW!!!
Lets hope it was not anything important .

 

The answer is easy, 309L. 309L will join most stainless to stainless joints as well as join mild steel to stanless and it even works for welding cast iron. If you know the composition of the stainless steels being welded, then yes 308L could be used for joining 304, 316L should be used for joining 316. You can potentially safe a few dollars using 308L on 304 and 316L gives better corrosion resistance in it's applicatoin but 309L typically works well enough in most applications.

 

I normally say 308L as it's the preferred rod for 304to 304 and 304 to 316, it can be used on 316 to 316, but of course it will have lower corrosion resistance. If it's a mystery piece of stainless, than it probably isn't critical enough for people to care about corrosion resistance.

308 is the goto rod for stainless to stainless in the 300 series. 309 is the goto for everything and stainless to steels. But they are both interchangeable for non-critical stuff.

 

The rail guys at work use 309L-16 for joining switch gear to tracks and H sections.

 

Know your base material before you choose a rod. If that information is not available, take a magnet to your source, and confirm if it is magnetic. If it is, you can basically follow what others have previously posted, however, if it non-magnetic, that would indicate your dealing with a 400 series stainless, and you must adjust your rod accordingly.