I contacted Castle Creations and Neu Motors with my concerns about the 1/8"/3.2mm shaft. Part of the issue here is the Tru-Turn spinner, which clamps on to the prop shaft fairly far out and even when fully bottomed out it leaves the first 1/4" of the motor shaft exposed. I imagine the spinner also somewhat larger/beefier than what typically might be used on this size motor. In the event, after explaining all this to the nice folks at Neu Motors, they have graciously agreed to build me up a new motor with a 5mm shaft free of charge. They really stand behind their products, and beyond that in my case, they obviously really care to see their customers succeed. THANKS NEU MOTORS!!