i have a 2001 f150 reg cab,lwb with the V6,just had the "pleasure" of having to change the brake line going too the back axle,my question is,why would the designers at ford use a brake line with a metric fitting on one end and a sae fitting on the other end,i had to use 2 pieces of brake line (one 72" and one 8 ",actually i could have used a 6" piece,but didn't want to make another trip to the parts store)


ok,i feel better now

 

you ever meet an engineer with common sense? i havent..

 

As far as I know the fittings are metric. A 3/8 inch fitting will screw into a 10mm but it will leak. I find it highly unlikely that the fittings are mixed but I have never checked. I have had to replace the flex lines in front but I purchased the complete part and it simply bolted into place.

 

mine has the 3/8 inch fitting at the back axle and a 12mm fitting on the front,i bought the truck used so i thought the brake line had been changed before and pieced together,but it was factory line and all one piece.

 

I've worked on a lot of brakes and never seen a 'factory' mixed SAE and metric. I don't doubt you have this, but I suspect some previous owner/shop did a hack job on it.
As you point out....it makes no sense to do this.