I don't think that bit of white (I'd guess bone) on the D'Isanto above is original; it looks rather amateurishly shaped and doesn't look like the typical method for doing such things. #Very early on (from the first Neapolitan instruments into the mid to late 1800s), there was often an inlaid plate of pearl in mastic, ivory, or some hardwood at the butt to protect the table as the strings came off the hitch pins and over the top (see attached picture of my anonymous ca. 1835-40 French instrument, possibly from the Eulry shop). #By the late 1800s, as steel strings became more prevalent, those mandolins that still employed ivory hitch pins often had a little metal plate with a 90-degree bend in it to sit along the edge of the table and protect it from the bite of strings. It simply sat there, no formal "installation," held by string tension. #By way of example, it seems that Stridente made most of their instruments this way. #It looks like the UK D'Isanto on eBay has such a plate hiding under the probably non-original bit of plastic/celluloid. #Unfortunately, such metal plates would be even more prone to loss than tailpiece covers. #I understand fabricating metal with a bend along a curve is not an easy one-off type job.