These fittings should actually be 1/2” NPS/NPT which have an internal rubber seal or tapered seal and you don’t use ptfe tape on them like is shown in 2nd photo. While other fittings have same thread, they don’t seal the same way as the original fittings intended. Note the flare on the threaded side if you remove it. I use 3/8 CTS on other side which fits 3/8” pex B with a push in connector. For these types of push in connections you insert a locking clip after pushing in which may be what arrows in that 2nd photo show. Here is an example of the connector I am using to repipe my water lines:
I don’t have a lot of photos, but I have this.
View attachment 235367
I replaced all my water lines with 15mm lines.
Connected with John Guest connectors :
View attachment 235368
Don’t ask me why the red arrows are drawn in, probably for someone else’s reference. But they are 3/4”x15mm (hose push-in side)
Others will now have a point of reference now to direct you further. But in SBO Store on this site will have what you need.
Do you know if it’s the screw on fitting or the main threaded end that is leaking?
Hope this can help you.
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