Insertmaterial grade chart

I have a couple face mills that I use for mainly plain steel & sometimes stainless steel but I just use the same inserts for both kinds which doesn't work to well for long runs of the stainless. I've figured out a little bit from my machinists handbook and some websearching but I'm still lost as to know what to actually pick for the variables for different types of materials. For instance my one 2in face mill uses inserts

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Insertgrade chart pdf

I can figure out what the different letters & numbers mean but how do I know what angles & other things to make better for stainless? And why are there 2 numbers on this one pack? I'm mostly all self taught on machining so my knowledge is spotty and any help is very much appreciated.

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YG-1 Turning Inserts, Insert Style: WNMG, Insert Size: 080408, Material: Carbide, Width (Inch): 1/2, Length (mm): 0.307, Inscribed Circle (Inch): 1/2