Description
Same thread on both ends, 1/2-20, and a different flare on each. One side takes a factory bump tube, the bubble flare used on most metric hard line and plenty of domestic line too. The other is a male JIC 37 degree flare for aftermarket hose ends and braided line.
That combination is exactly the one people get caught by. Because the threads match, a bubble flared line will screw straight into a JIC port and feel tight, then weep under pressure, because a bubble seat and a 37 degree cone only ever touch on one ring. This adaptor puts the correct seat on each side instead.
The usual reason to want one is keeping a factory hard line you do not want to cut and changing what it connects to.
