Well, you learn something new every day...
I'm redoing my J-20's brakes, stem to stern, as its life as a plow-truck was not kind to the lines or to the components.
Replacing the rear wheel-cylinders, I decided I should replace the old bolts, as I had lost one and the remaining three ranged from crusty to crustier.
So off to Lowes I go, wheel cylinder and old bolt in hand. The front caliper banjo bolts, as well as the bleeders, are now metric, so I'm looking at the metric bolts, M8 seeming to be the right diameter, but the 1.0 pitch is too fine. So I try the 1.25 pitch thread; *still* too fine. The thread-pitch on the M10-1.5 bolts seems to match, so I start looking for some M8-1.5 bolts. They don't have them.
Nor does Autozone.
Nor does O'Reilly.
Fastenall doesn't open until tomorrow.
So, I give up, have dinner and get ready to settle in for the night, and start researching on the internet these metric-thread bolts that are all new to me.
But nobody mentions the M8-1.5 size.
Could it be?
Out to the garage, where I have plenty of standard-thread bolts.
And sure enough; 5/16-18 it is.
So off to Lowes, who has plenty of grade-5 5/16-18x3/4" bolts that I can grind the tip down to the proper 5/8" length tomorrow morning.
So *some* aspects of the 1987 J-20 braking system are metric; the attaching bolts for the rear wheel cylinders are *not* among those parts.