Which Chain? (Chains / Size / Width / Wear)

Rear axle snapping usually only occurs on cheap hubs because the bearings are placed just on either side of the hubshell leaving a massive overhang of unsupported axle inside the freewheel/cassette.

Shimano hubs have bearings right at the edge of the freehub so it is supported at its two ends of the axle making snapping very very unlikely. Just a tip for the future.

Thanks for info. I learned this yesterday too when swapping out the axle. This was definatley the cause. The break was in the exact middle of the unsuported area. All the more reason to not have a cassette / gears . Its also been supporting the extra weight of a toddler in child seat for the last couple of years, so I'm sure that's added to the wear.