I have some inline filters that have male foster on one end and female foster on the other. It took three tries with PA to get one where the fosters would couple.
Apparently there isn’t a standard drawing available for shops that make fosters where the tolerancing is correct to allow any foster to connect with any mating foster regardless of who manufactured it/them. The theory of interchangeable parts was invented by Eli Whitney in 1798 and then further and precisely developed by Honeywell with the advent of GDT (Geometric Dimensioning and Tolerancing) where if toleranced properly parts can be manufactured anywhere in the world and they will mate as designed.
Makers of fosters around the world seemingly sometimes reverse engineer a part by measuring a supposedly good part and duplicate it. Unfortunately reverse engineering gives a specific size but a necessary tolerance is guessed at. So some will mate, some won’t.
Sometimes a male just needs a little polishing the one diameter so it will fit in the female (in my experience). But if it’s the ball groove that is the bad actor it’s possible the fitting can, as Spacex calls it, experience an “unscheduled rapid disassembly”. Not good.
Bargain fosters can be a non-bargain.
It’s hard to tell if you’re getting a quality one or poor quality one.
Try ordering another one.
