Thanks cowboy, I don't know why when I put in stepped ring mandrels in amazon I wasn't getting anything close. That is the thing I need but it's sizes are quite limited, And it's not a UK one, It might do anyway, but it will mean having to change sizes each time by 20th inch or so as converted most uk sizes end up with 1/4rs and 3/4 sizes.
The second link doesn't allow much in the way of space when braiding leather rings around it, so it's not so good.