Brake Fitting Size metric vs AES in different years?
 

I'm looking at the passenger side brake line to hose fitting in this '88 k2500. The hard line got cut, so I thought I would get a replacement line from the pick it yard. I think it was from a '95 k1500. It connects to the T as it should, but the other end at the brake hose it binds. It looks like the one from the '88, but I'm thinking one is metric. I looked on the parts houses and they show 3/8 -24 for the hose on both '88 and '95. My next step is to remove the hard line and take it to my flaps to match it to an adapter. Thought I'd ask here before doing that. Is the fitting on the end of the hard line 10mx1 for some '95?

Re: Brake Fitting Size metric vs AES in different years?
 

Both should be metric, but the size may be different for the 1500/2500 since they have different size brake calipers

Re: Brake Fitting Size metric vs AES in different years?
 

Mine's a 2500, not sure on size, but I think Bill is right about them being metric. Maybe the truck in the bone yard had some cobbling going on. That's odd the listings call for SAE

Re: Brake Fitting Size metric vs AES in different years?
 

The parts store had a F-F adapter with M10-1.0 and 3/8-24” so with that I was able to confirm the brake line from the ’88 is 3/8-24” and the brake line from the ’95 is M10-1.0. (I hope I didn’t get that backwards). They didn’t have the adapter I need so I ordered one for each end. I’ll bring the lines to confirm when the parts get in to the store.
When I removed the line from the brass T, it was snug, so I must have use a heavy hand to install. Makes me think that end is metric on the line fitting. This used line accepts a 14mm wrench and a 9/16” wrench is loose. The old line from the ’88 accepts a 9/16” wrench and the 14mm wrench is too small. I checked the line on my 1990 k1500 and found the 14mm wrench too small, 9/16” wrench fits. Then I looked at the ’88 k2500 at the brass T the fitting from the driver side line does accept a 14mm wrench, but I can’t confirm what the threads are. I looked on-line some more looking at the hose since there is specs listed for that, and every listing shows 3/8-24” where it connects to the line, and 10mm at the banjo that connects to the calliper.
This front line is 7’ long with over 20 bends, the used line that I bought does not appear to be cobbled. The O-Reilly’s website has a listing of every vehicle the one part will fit on, it looks like they were all SAE, but I couldn’t locate a metric brake hose. LMC has three listings for the set of brake lines: 88-89, 90-94, and 95-98, but no specs.
The local parts stores don’t seem to carry a pre-bent line, only straight pipe with fittings, and only up to 6’. Or I could get a roll and flare the ends. The on-line retailers that do sell pre-bent lines only sell as a kit, and they don’t list the specs, so I can’t tell if the fittings are metric or SAE, just that they fit my vehicle. 3/8” = 9.53mm (.3750”) and 10mm = .3937” so the 10mm fittings will screw into a 3/8” socket.