Changing of mind here, we aren´t going to the beach anymore.  Talk about wife´s stubborness and wishing things made in a snap!

   Back to needle size - you are right, to me "diâmetro" is a good word.

  As a layman I would say "tamanho da agulha", however certainly is not being used outside of the layman and everyday chatting.   Yet, it is my opinion, lacks confirmation of native people or of a professional of Health.

   PP.