Small ring shaped winding key is a replacement for most Wittner Pyramid and animal-shaped metronomes that originally had this style of key. If your Wittner originally had a "football" shaped key, this one will probably fit, but the cover of the case may not close properly as the key's shaft is longer. In such cases we suggest the football key, #45678. For Wittner Series 800, 810, 840-855 metronomes, including all Pyramid models.