Ring 1 is your top compression ring, is closest to the crown of the piston and is 1 mm thick. Ring 2 is below that one and if I remember is 1.2 mm thick. The oil ring is the bottom ring and 2.8 mm IIRC. You didn’t make mention of piston or ring brand. Usually when you buy a piston set it will include gapping instructions and are usually pretty good guidelines. I recall my CP piston gaps being tighter than those linked. 0.021 for top ring and around 0.025 for the middle ring. I’d have to dig up my notes. As a genetal rule larger gaps tend to be safer but result in more blow-by.