Can anyone help me out, just got a set of mainspring winders with no instructions. I understand the principle but how does the new mainspring attach to the 'arbor' of the winder to get the new spring into the winder before dropping into the barrel

Terry, the end of the winding arbour should have a 'hook' protruding from it which locates in the slot in the end of the mainspring.
This pretty much replicates the hook of the barrel arbour.
As you wind the arbour, the hook will (should) grab the edge of the eye causing the spring to be wound into the cup.

Sometimes the small loop on the end of the spring isn't closed up enough causing the end of the spring to skip over the hook - you may need to either fiddle the spring onto the hook (if you can get to it) or close up the end of the spring slightly - if you do this though be careful - it's very easy to fracture the spring across the eye where the arbour hook needs to locate.

John

Thanks John (again)!
Much appreciated

Terry