All Vaisala sampling cells have ISO G1/2" parallel thread on the probe connection point. A sealing ring must be used between the mated surfaces of the sampling cell and a probe or transmitter with parallel ISO-threaded fitting body.
For device-specific installation instructions for the sealing rings, see the user guidance of your probe or transmitter at docs.vaisala.com. Sealing rings are available to order from store.vaisala.com.