Maybe to help - I have never worked with World Class bases before - mostly Weaver stuff. On Brownell's website they used to have (maybe still do) a spreadsheet showing dimensions of the various bases - curvature that they were cut to fit, spacing of the through holes, etc. Apparently the idea was that any ring with that spacing dimension would fit on that rifle - but some brands bases needed their brand rings to work (example Parker Hale) - some did not - so, could "mix and match" Redfield and Leupold "turn in" style, for example. The rings should be identical to each other - any height difference is done with the bases - not the rings - of course, Ruger had to be different about that. But Warne, Leupold, Tasco, etc. all seemed to make rings as same height pairs - is possible that you may want or need taller or shorter rings - depends on the mounting on the rifle, the clearance at bolt handle, the clearance above barrel. The very best is as mentioned above - a number or mark that identifies what it is for - then knowing what brand it is, one can usually find a reference to say what the base is used for - note that some bases are used as a front base on some rifles and a rear base on other rifles - goes to the mounting hole spacing - not just the curvature underneath the base.