Size of rings are 30 mm - to fit the scope body. Height of rings - almost every maker has different dimensions. "High" or "Med" for one brand often no where near same height as "High" or "Med" for another brand. Is a thing to start with blocks or shims - two, of same height - set on the picatinny rail - set scope on top - roughly to the required eye relief - adjust with more or less height - same for front and back - to get clearance that you want for Objective to barrel at the front and Eye Piece to bolt handle at the rear. Measure the blocks - look at various makers and find out how they measure their various height descriptions. Had read of same being done with plasticine or modelling clay - much harder to get front and rear to exact same height, which your ring set will be.