Silk
... that the last Silk motorcycle ever built was a 500cc model based on a prototype that was never produced and was used as a competition prize?
... that the last <b id="mwGNk"><a href="./Silk_Engineering" id="mwGNo" rel="mw:WikiLink" title="Silk Engineering">Silk</a></b> <a href="./Motorcycle" id="mwGNs" rel="mw:WikiLink" title="Motorcycle">motorcycle</a> ever built was a 500cc model based on a prototype that was never produced and was used as a competition prize?