Why are the front and rear ports on a MC different sizes?

[66coupe351]

Working through re-doing the brake system on my '66 and have discovered that the front and rear outlet ports on the dual-reservoir MC are different sizes. All of the old brake line connections on the car were 3/8".

On this MC the front brake port(on the rear half of the MC) is 3/8", but the rear brake port is slightly larger - maybe 7/16", not sure yet. The actual fluid port that the flared line matches up with appears to be the same size on both of the MC outlets.

1) Why would they have different sized threaded connections on these two ports?
2) Anyone know what size the rear port is?

Something else that is making this whole process more complex: I'm trying to use a combination valve. This valve has 5 ports on it that are 4 different sizes! The two front outlets are 3/8", but then the rear inlet port is a little larger, the front inlet is a little larger again(appears to be the same as the MC rear outlet), and the rear outlet is even larger. Why would they do this?

 

[Edbert]

Why would they do this?

So you don't hook it up wrong on accident.

 

[brianj5600]

So you don't hook it up wrong on accident.

And still in use today!

 

[66coupe351]

So you don't hook it up wrong on accident.

I had considered that, but thought there was probably a more complex reason.

 

[67CoupeDriva]

Ensuring proper connections is one part of it. Another is getting the correct amount of fluid volume and pressure to the appropriate systems. The rear brakes exert less stopping power than the fronts, and the fluid volume requirements will be different if you happen to have a disk/drum combination. I let them smart engineer fellers have their credit, and don't try to second guess 'em.

 

[krash kendall]

It's the same reason no two electrical connectors are the same on a modern wiring harness. When I swapped the engine in my wife's Sprint for the first time the whole job took four hours from a turn key car to a turn key car (I really needed the car that night, but it no longer had enough compression to start and I broke the output shaft of the tranny in my Jeep picking up the motor that day.) . The systems were idiot proof! If you have ever played with a Tupperware Shape Ball you can swap a new motor, there is no question where things connect.