Mystery in a Small Case: What Was This Ingenious Tool Used For?

The sharpener is compact, with a small case and a distinctive red cord. The two brass pins inside the sharpener spin when the cord is pulled, causing a mounted blade to rotate back and forth against sharpening surfaces. This motion would gently hone the edges of a reusable  razor blade, helping to extend its life. For decades, this device was a cost-effective way to maintain blades and avoid the expense of constantly buying new ones.