Technical question for sewing people

A couple of years ago I found a large conical bobbin of fairly thick thread in a charity shop. It wasn't labelled. I can only describe it vaguely - the thread was about 1-1.5mm thick, shiny, seemed to be VERY smooth, was reasonably strong (I think the breaking weight was 4kg or so) and turned out to be absolutely perfect for things like pendulums, pulleys, etc., which was obviously not its intended use.

We used up the last of it a couple of weeks ago, now I'm having real trouble finding anything as good to replace it. About all I know is that the bobbin was about 8-10" high, formed round a cardboard core, I think it was intended for some sort of heavy-duty sewing machine.

Anyone got any ideas what I should be looking for?