Abstract: A ribbon spring for use in a sprag-synchronized one-way clutch includes a metal thin plate which is formed with a plurality of sprag insertion holes of a predetermined shape preferably defined by stamping. In one embodiment, the sprag insertion hole is generally E-shaped as defined by a pair of tabs substantially identical in shape and size which extend into the sprag insertion hole from one side edge thereof. In another embodiment, the sprag insertion hole is generally C-shaped as defined by a relatively wide tab which extends into the sprag insertion hole from one side edge thereof and which is formed with a slot. With these structures, the sprag is prevented from wobbling or skewing during operation and an optimal spring constant can be set easily.