The Danfoss 087B1190 stainless steel pocket is an accessory designed for the
  ESMU-100 immersion temperature sensor in copper design (code no. 087B1180). The pocket protects the sensor from direct
  contact with the medium and allows easy replacement without the need to drain the system.
  It is made of AISI 316 stainless steel, ensuring a long service life even
  under demanding operating conditions in heating and cooling systems.

The pocket is installed in pipework or a tank with a G 1/2 A thread. It enables measurement of the
  medium temperature (water, heating fluid, etc.) in heating systems, solar circuits
  and other HVAC applications. To ensure optimum heat transfer from the pocket to the sensor,
  the use of thermal paste is recommended (available separately, code no. 041E0110).