There are two distinct types of ring sizers with completely different uses. One type, which you're more likely to see if you're interested in purchasing a ring, consists of a number of small metal objects that look like lens-less magnifying glasses of slightly different sizes attached to a chain. The other type is a tapered metal stick that has small grooves at various widths corresponding to ring sizes.
Finding Your Ring Size
If you are unsure of the size of your beloved's finger and want to order her one of RedEnvelope's rings, take her to a jeweler. He will use the first kind of ring sizer mentioned above. Your jeweler will ask which finger she wants sized, then insert that finger into several of the sizers in turn. He will probably start a few increments larger than her finger and work his way down until he finds the one that fits her finger perfectly. This means it should feel snug but not tight, and she should be able to remove it easily but someone across the table should have some difficulty pulling it off of her finger. Your jeweler will then read the ring size on this sizer and inform both of you of her exact ring size.
Finding the Size of Your Ring
Maybe you already have a ringand you're curious to know its size. You could go through the hassle of finding a finger it fits, whether your own or a friend's, then using the sizer to determine the size of that finger. There is an easier method using the second kind of ring sizer. Simply slip the ring over the small end of the tapered stick and slide it down toward the wide end until it fits snugly. Make sure it is not loose on the stick, but also do not forcibly push it farther down the stick than where it fits comfortably. Read the number on the stick at the groove where the ring fits, and you'll know the exact size of your ring.
Making a Ring
Another use for the second kind of ring sizer is to make your own ring of a certain size using the lost wax method. Use melted wax to form a band around the stick at the correct size. Then, using slightly heated metal instruments of your choice, melt and shape the wax into the style of ring you desire. If you are using any gemstonesin your ring, you may insert them at this stage as long as you want them to be held in place by the metal in your finished ring (for example, you may want silver to cover opposite corners of a gemstone to hold it in place). When you are content with your ring, very carefully remove it from the ring sizer and take it to a jeweler. The jeweler may be willing to cast it for you, but if not, then the jeweler will be able to direct you to someone who can.