The thermal link comprises of a brass tube with a brass
  element soldered over it. This combined component has
  been designed to alleviate possible linear creep of the
  soldered joint. The component is then inserted into a
  13mm diameter zinc plated holder which screws into the
  locking assembly from outside the case. This holder has
  an integral 4mm zinc plated pin fitted to indicate if the
  thermal link has been activated by an increase in induct
  air temperature.