Thanks for the reply. I have looked at them but they are too shallow to take any decent amount of thread. I got a 35mm film spool but it's construction prevents a bolt going through it without too much faffing about. I guess I will have to wait until each serving spool is empty and then refill it.I was going to suggest cotton reels.
Thanks for the offer but is too much trouble for such an item. I have some experience of 3D printing.Sounds like something I could help with.
Happy to have a go at designing and 3D-printing a test piece for you. Have you got any pictures/dimensions and I'll have a look