Banjo nut connector used in older cars for the first iteration of fuel injection. Inner eye - 8mm, outer eye - 20mm, barb di - 6.3mm.

My problem was that I have a 1987 VW GTI with CIS-E fuel injection. One of the first iterations of fuel injection. While rebuilding the car I ran into numerous issues with fueling and, naturally, went to test the fuel pressure, which is vital in these older fuel injected cars, and found that without a VW specific fuel pressure tester, there was no way to do it. The tester ended up being around $800 IF you could find it. I decided this was ridiculous and that I just needed a banjo nut with a generic 1/4 hose adapter to test. So I fabbed it up, tested the size and all is good.