I believe it is 5/16? Put a open end 5/16 box wrench on it to double check it. My rear was brittle on the rear axle end. I replaced the hose with some outboard fuel hose I had. Not ideal, but better than old and brittle.

 

shipping adds a lot.......

 

that's funny...I was thinking about fuel hose as well!

 

Not if I drive to one of the Ford dealers within 10 miles and pick it up from their parts counter.

 

Yes that will save shipping.

 

Yes. If there's a cap dirt wouldn't eventually plug it up. I'm trying to find a breathable cap for mine as I found mine plugged up with dirt.

 

When I had my Frontier, I relocated the short breather hose with a longer one to the cavity behind the passenger side tail light assembly and clipped it up there with a filter on the end. Fuel hose works just fine.

 

Did the same to my Titan. Those rear axles were known to blow out axle seals because the differential vent would clog up.

 

Yep.