Ruger rings are number 3, 4, 5,& 6, with 3 being the lowest and 6 being the highest, A #4 is .125" higher that a 3, a #5 is .125" higher than a #4, and , of course, a #6 is .125" higher than a # 5. The .125 is the difference in height on the M77 between the front and rear receiver. The #1 uses the same height rings as they mount on a 1/4 rib. Use #3's for straight tube or up to 32mm scopes #4's will work with most 40mm objective end scopes, and #5's and 6's with really big objective scopes. Getting the proper eye relief can sometimes be a problem with a #1. Mini's and M77-22's are the same a s a #1. Bob! 8)