Actually the mandrel was very generously gifted to me by Travis
It is great to get a gift, especially following putting some time in to help - but I don't normally expect it - a "thank you" and "helped by" is fine.
Previously, to make these
I used to tie them by making a small square piece of wood of the perfect circumference with loads of thumb tacks.
But often the pins needed to be too close together so sometimes had to carefully use 1 pin for 2 nested bights - then if I used the mandrel a second time for a second fid then the pins start falling out - so this mandrel will be so much better if I want to make the same knot repeatedly. So it will be interesting to have a go with this new mandrel now - feedback/conclusions to follow.....