Nut 1/2 inch plastic with internal sleeve, PN 41056, used on / with the 1/2" 1710 brine valve and tube.
1710 Series Brine System for the Fleck
One used on back of 1710 brine valve to connect to the Gray tube, and one used on 1/2" brine tubing to salt tank.
# 15 in our diagram
Brass Insert, and other parts sold separately.