This RepRap Power Ring can be set to use "standard" ring sizes for around the world. Instead of having to enter the specific measurement you can simply select your region (there are 4 available) and then enter the ring size appropriate for that region.So if you need a size 13 ring in the US, then the first parameter would be 0 (setting the region) and the second would be 13 (setting the size). There are 3 other parameters for things like thickness, depth of the logo, and whether the edges are beveled or not.NOTE: The .stl is just a sample that creates a ring in the US/Canada size of 13. To set your own size edit the OpenSCAD file, render, and export your own .stl.There are 5 parameters to set in the OpenSCAD file to customize the ring.1) Sets ring sizing region. Values are: 0 for United States and Canada 1 for UK, Ireland, Australia & New Zealand (Please note: "" is needed around non-numerical values) 2 for India, China & Japan 3 for Switzerland 2) Sets internal ring size based on ring sizes for the region set in parameter 1. 3) Sets thickness of the ring (lengthways along the finger). 4) Sets depth of the RepRap logo embossed on the ring. 5) Sets whether the front edges are beveled or not.