A ring sizer is a device to measure your ring size. There are different ways to measure your ring size. A jeweler, for example, has a set of metallic or plastic rings, which are listed from small to big, in order to figure out the right size. If you already have a ring that fits well, you can use a ring stick where you slide the ring on and simply read the ring size. The plastic ring sizer, whom BAUNAT offers for free, works rather like a plastic little belt that you turn on your finger, after which you can easily read your personal ring size.