their online store), & other suppliers of repute, will have a certificate to go with each spool of wire which they sell. It gives a real measure of the physical properties of the wire. Much like a Proof Certificated does for a batch of chain.
Read the section of this page, in the upper left hand corner, entitled "Buying Wire". Rigging Only's 1x19 stainless wire is type 316 for standing rigging and can be used with swage fittings and mechanical wire terminals
It, the whole page, as well as their site/catalog, is educational.
As a bit of "self help", you'd perhaps be wise to do some studying on the physical aspects of rigging, it's components, as well as the "how's & why's" behind rigging.
Don't be shy about calling various rig shops with questions, or especially paying them visits live. The latter being the best way to absorb knowledge from them, other than learning
Avoid being a pest (if you stop by); but they'll get it if you truly want to learn. As they know that perspective customers who have good experiences with them, even if you/said customer doesn't buy from them (this time). That it's likely that you'll refer other's in need of rigging their way.
I've been doing as much with my favorite rig shop for 25yrs, even though they've not seen my face for half that long.
Also, Brion Toss, a rigger of some note, has a new edition of his book The Rigger's Apprentice
slated to be released soon. Not that his other (current) one isn't chock full of good information. That & there are some bits of wisdom on his website, & the forums
there - www.BrionToss.com
I'd Definitely suggest picking up a copy (new, old, both, & or several of his works). It's $ fairly well spent in order to make more educated purchasing
, & rigging decisions.