You forgot to mention the alloys You will be welding. 310-15 is not a really common rod that You will find in hardware stores. 304 is commonly welded with a 308 rod, 316 is normally welded with a 316 rod, and stainless to carbon steel is often welded with a 309 rod. -15 is DC only and -16 is AC or DC. These are basic guidlines for non-code work, hope it helps.