Clock Mainspring Winder. This is a new clock mainspring winder. It measures approximately 3 15/16" x 2 7/16" (100 x 62 mm). We work hard to update our descriptions and pictures of our merchandise. As part of a process of ongoing innovation by our suppliers, newer versions of the item shown may be shipped before we are able to complete an update. As a result there may be a slight variation in color and design.