“Standard “ marine snaps are called by several designations: line 24, 24 ligne, 0.600”, or 15mm. There are five common pieces to a snap set, if you include the screw in option for the stud. You only need the cap and socket.
Use stainless, your best option for actually getting stainless, instead of some junk, is to buy from Sailrite , or stick to Dot brand, but avoid Lift-the-Dot, which is a specialized snap, which only works in one orientation.
The vice grip snap setter is a handy tool to have around, but the key to getting good snap sets is having the correct barrel length. All of the different types of setters have a limited amount of flare, and if the snap set is not snug to the material at that point, then the barrel collapses to one side. This is especially true with a cap and socket, where the barrel length only needs to be roughly the thickness of the material, and the flare will pull the connection snug.
Start with 3/8 inch, and if the snap does not pull snug with the flare, or if it collapses to one side, hold the next cap In a pair of pliers, and touch the barrel to a sanding wheel to shorten it. Don’t worry about the rough end, it will flare smoothly. I’ve done this more times than I can count.