Rolf,
I have made two snuffer rings from carbon using different methods looking for the best option.

I will be giving the aluminium option a go because I think it will be simpler.
The mould to bend the alunminium tube around would be dead easy to make and once made all your mates could use it to make their own. So you don't need fancy bending gear in a machine shop. I expect once the mould is made, apart from the welding of the ring to pole or sleae, you would spend around 10 mins on each one.
Anyhow I'll let you know as soon as I get a chance to give it a go.

Regards,
Phill

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!