6 mm barb fitting, also called a non-return valve. Found in the 85 S and E, 85 Leva, 95 and 105 models. This valve is designed to expand and open at 12 + bar. If water is leaking through it at less than 12 bar, and adjusting the screw does not resolve this, it must be replaced.
Attention CA Residents: Prop 65 Warning
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.