Propsaver - model plane prop saver for 3mm shaft and m3 drive nut

Prop saver - print then run a 3.5mm drill bit through the hole (by hand usually)
fits on 3mm shaft with 1x m3 nut driven into the propsaver.
Then loop a rubber band (a o-ring works well) round the prop and prop saver to hold the prop on, hopefully allowing the prop to come off in a crash without breaking the driveshaft or prop.