Captive Ring Tool
There are many ways to cut captive rings and specialty tools are sold to accomplish the task. I decided to make my own captive ring tool from an Allen wrench, the tricky part being the shape of the grind. I tried many different shapes without success before hitting one that worked. The various grinds were tried using a grip lock pliers to hold the wrench while proving the design. I cannot give exact details on the tool other than show you a close up of the cutting edge. The tool is capable of cutting captive rings extremely close to the stem and the under side of the ring is nicely radiused.