A "push knife" mounted in a wooden handle. The tip is a bevel-sharpened blade, bordered by a fence ("safe edge") set a right angles to it, which acts as a guide.
The purpose of the tool is to cut "feathers" round the edge of the insole. These are grooves made during the "making" process when the upper and welt are being stitched to the insole.
Vertical cuts are first made with an ordinary knife round the edge of the insole; one at about 1/8in(4mm) from the edge, and another at about 3/8in(1cm) from the edge. This distance is dependent on the size and type of shoe.
The edge or the upper will eventually lie in the outside feather; and stitches will by sunk along the inside feather. After the Feathering Knife has cut away the unwanted leather fron both inside and outside feathers, the space betwheen, known as the "holdfast", is left standing.