Abstract: A tool, an attachment head and a power tool system, each for working on contoured surfaces, are disclosed. The numerous embodiments of the designs are made possible through the use of flexible structures that exhibit a phenomenon known as the “fin ray” mechanism because it was first observed when studying the motion of fish. Similar to the fish fin, the working surface of the disclosed tools behave unexpectedly when a lateral force is applied: they do not bend away, but curve toward the applied force. Generally, each “fin ray” tool includes at two flexing sidewalls or members joined at their tips to form an acute triangle. A plurality of struts hold the members apart while allowing elastic movement. The curve of the working surface allows the tools to provide greater contact on contoured surfaces.