Using a Stanly blade..scrape away the old epoxy...and remove the old whipping..
Inspect and clean up the area to be whipped...
Secure the new ring in place with a bit of tape..and begin whipping on the new thread..from the blank towards the foot not on the ring foot...
Once the ring is whipped on coat in epoxy resin and keep turning the rod until it drys..approx 5minis the epoxy type to use..one minute is too short and 15 min too long..
The finished repair...almost as good as the factory finish and just as strong!
Lots of internet stuff out there on this so have a detailed look first...i repaired two beach caster rings years ago and their still good....( sorry about the poor pics)