Sprocket nut...

[Grahamm]

I went into an auto factors and asked for green loctite (270 according to Google) " what,I've never heard of that" was the reply
So he sent me to an engineering/agri supply place nearby and when I asked for "green loctite, 270" that was what I got.

Hopefully it's not overkill strength wise or I'll be cursing myself when i go to change the sprocket...time will tell I suppose

Interesting, I'd never heard of Green Loctite.

According to this page Green Loctite isn't as strong and doesn't have as high a temeperature range as Red Loctite, but it's low viscosity, so it can be used on a part that's already secured without needing to undo it, like Plusgas it seeps into the thread.

Apparently it can also be removed with heat like Red Loctite, so you should be ok getting it off in the future.