FWIW -- something about the way the original question was worded gives me the impression that Grey Whiskers might not have been sure what a sideplate actually is -- not merely where it's located. Just to clarify that, not to insult anyone's intelligence -- a sideplate is a flat piece of metal, taking various shapes and usually made of the same material as the buttplate, triggerguard, and other hardware, that serves as a glorified single washer or pair of washers for the bolt(s) that pass through the stock and hold the lock in place. It isn't part of the stock per se. The shape and size of sideplates is one of the factors considered when attempting to determine the age of an original long gun.