For Rancilio (and Promac/Laranzato) ONLY. Larger than the more common W_517, 1/4" valve. Allows air to escape as the the boiler heats up. OUTSIDE diameter of the male thread measures 5/8".
The W_154 gasket is your best option for this valve.
WARNING: This product can expose you to chemicals including lead, which are known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, go to www.p65warnings.ca.gov.