A variation on the same question - if a screw is missing, but you don't know the thread pattern, exact length, diameter, etc., what's the best way to find out? I have several rifles that have been drilled for scope mounts and I'd like to at least hide the ugly holes by filling them with well matched screws. I assume one needs to order an assortment from Brownell's and do it by trial and error, or buy some kind of expensive gauge?