ring to get stuck on the rod when it contracts during cooling. Another tool that sounds good on paper but maybe not so good in practice.
Since nobody else has mentioned it, I will… All the mandrels I’ve
ever seen aren’t just tapered, they are ~strongly~ tapered. That
means that if you use it to solder two rings together they will be
off-center - if you use it to solder wirework “in the round” it won’t
be a cylinder, it will be a cone… If it’s good for you, then it
is. Mine stays on the shelf 4 years out of 5. Every once in a while
there’s something it works for.