title_body: Foam knife one on Breville dual boiler?
upvoted_answer: Unfortunately, from some quick research, it looks like the Breville Dual Boiler has a steam arm that possesses a female thread where the steam tip is inserted into the steam arm.
  
  However the Foam Knife 1 Steam Tip you linked looks to also possess a female thread which means that it cannot be fitted on to the Breville Dual Boiler without modifying the steam arm in some way or replacing the steam arm for another compatible one that has male threading.