So. I was changing my chain the other day, routine job, as you do.
I put the nut back on the ale, and started to tighten it up, as again, you do.
Then I started noticing how long I'd been sat here for, tightening away.
As it turns out, the previous owner hadn't used a high-tensile nut on the axle, meaning I've completely threaded the nut. It's now SMOOTH inside.
So, my steadily-more-urgent problem now, is WHERE DO I FIND ONE QUICK?!
It's an M18 x 1.5 nut.