These have driven me crazy. Spent many hours, and many quarts of brake fluid before knowing that they were there, both in SS brake lines, and clutch line. Got them from a vendor. Every time I think it couldn't be that stupid little ball that is causing me so much trouble in bleeding, there it is again. What the heck is it for, and who is crazy enough to put a HOLE in a brake/clutch line?!
The question is how do you seal the darn thing off? On some of the fittings I am using you can flip them around and that will work, others you can't.