OP - you are going to discover that various makers have different ideas what is Low versus High rings - not even close to same hieght, one brand to another. You will want an actual dimension - often from top of flat of base to bottom of the scope body, although some makers give you a dimension to centre of scope body. Most definitely helps to have a buddy who has identical scope installed on identical rifle and get that brand and size of rings - there are substitutions that work well, but beware that not all brands are the same dimension - "Low", "Medium", High, or "Extra High". On some old school rifles, concern yourself about bolt handle clearance - there was at least one BRNO .22 here that had nice clearance to barrel, but the bolt handle would hit the eye-piece, with Warne brand " Medium" rings.