I seem to recall from one of Carroll's book that he started using AN nuts and bolts because 1) they had consistent quality control and intelligent shank sizing and 2) he could get them by the ton from surplus stores. You certainly can't complain about that. I expect the hydraulic fittings followed the same logic.
In my example of the brake proportioning valve, that's something that should ideally pop in place of the factory part. Just bolt it into the existing hard lines. So that NPT-to-metric adapter is critical. But it's simply a part that doesn't exist in nature. This is the sort of problem that drives me nuts. If you're modifying production cars, you have to keep converting to and from AN even though production cars are pretty consistent. WHY is it so hard to find metric brake parts? Quick, name a vehicle made in the last decade that uses SAE flare fittings.
On my MG project, I have Miata calipers and a Wilwood master. So metric fittings on the calipers and I have one of the few Wilwood masters with an SAE flare right on the master. I also have access to a large collection of SS lines with plastic sleeves that were assembled by a pro, not the guy at NAPA who was given a 5 minute lesson from a guy who got a 5 minute lesson from a guy, etc. So I'd like to use those.
So far, so good. Both the metric and the SAE flares use a 45 degree cone, so I just have to remember to slip the correct flare nut over the tube. Since I'm building my own lines, the rare (but easily accessible to me and me alone) NPT-metric adapter is not a big deal at all, and I can make all of the flares SAE except where they have to fit up to the front lines. But in the rear, I have a banjo fitting to deal with and a solid axle. No need for flex lines here, right? All I need is a banjo to flare adapter. Great. I have several to choose from, all at different angles. But they all have *#@$ AN fittings on the other end, and they use that different flare angle. So either I have to get a new flaring tool, stack up adapters or find a different option. I'm finally solving it by using an off-the-shelf SS line with an AN fitting on the other end and an AN-NPT adapter into a tee. It means more junctions and a section of flex line where none is required, but this way I can actually put it together with what I have access to.
If I were building a full-on race car with all new bits, it would be a different matter. I could throw away my 45 degree flare kit, get a 37 degree one and a wall with a big pile of AN fittings. But I have this tendency to modify production cars, and AN flares remain a pain in my patootie. Someday I'll spend another pile of cash on a good AN flare tool and this will become less of an issue. But right now I'm just angry at the performance industry that has settled upon a "standard" that is only found in the performance industry, and not on the cars the performance industry is modifying. Add to that the fact that you simply can't find AN bits in this town, so any time I need a fitting I have to wait for UPS to bring it in.
My fuel system is all AN. That was easy enough, although I had to keep ordering in the perfect fitting - I seem to have an appetite for 45 degree bends, for some reason. That was fairly easy because the whole thing was basically built from scratch, and push-lock to AN adapters dealt with the connection to the fuel rail. My PS system was also straightforward, once I laid my hands upon the custom AN-to-Miata-rack fitting found only on the shelves of FM. But sweet cheesus, the brakes!
Okay, rant over. Sorry, just had to vent.
