Finished the combined retainer ring / coupler for the KILO 12G “lite” motor. The coupler was made from 80x5mm tube and almost a direct fit into the 86x3mm casing. It is a bit beefy. However lets first see how she copes with the 96bar MEOP and the countersinking of the 86x3mm casing which will probably extend into the retaining ring / coupler effectively reducing the threaded area. Also I didn’t have a boring bar long enough, or even bothered, to bore out a significant weight saving from the inside. KISS. After a succesful flight it can potentially be optimised to a 80x3mm coupler.