The Unchamfer tool turns a chamfer into a hard edge.
Poly strip - a row of polygons - along the chamfer.
The best way to select a chamfer is usually by loop selecting it - by default via
Alt + Select Mouse, while pointing at an sweep edge of the chamfer.
The sequence of the chamfer polygons determine the direction of the hard edge. If Unchamfer is run on a single polygon, the direction will be determined by edge length, but can can also be reversed in the redo/tool properties panel.