Replacing my stock fuel lines with AN lines, and have to adapt from the stock hard line which (from my understanding) is 5/16. Come to find out, the 5/16 to -6AN adapter that I bought, doesn't fit over the stock hard lines. Am I missing something? Am I doing something wrong? Any pointers would be appreciated

 

The stock hardlines are actually 8mm (~0.3150"), not 5/16" (0.3125"). For most applications, i.e. rubber hoses this difference is negligible, but since the compression nut is designed with a tight tolerance the difference of ~0.0025" might be preventing it from sliding on.

If you hadn't already cut the flare off the line I would have recommended a 6 AN to 5/16" hose barb fitting, and a short length of hose to connect the fitting to the hardline.

 

Ah how wonderful. Do you know if anyone makes an 8mm hardline to -6AN?

 

There are some 8mm to 1/4" NPT compression fittings on various non-automotive-specific sites, you can search and find them but I'm not sure I would recommend that approach.

Since the line is off the car, you could take it into a shop and have them put the bubble flare back on the end, so you could use a piece of 5/16" hose to connect to a 6AN to 5/16" hose barb adapter like I mentioned above.

 

The piece shown in the picture was a cut off piece I was using in order to test out the fitting. The actual hardline is still on the car. I do have a flare kit though. I can just flare that myself. Then I guess I can just buy a -6 female to barb fitting and run some hose like you said.

 

I used a Swagelok Stainless Steel 8mm to 5/16"? Female NPT fitting and then Aluminum male NPT to -6an.

Stainless fitting as to get a reliable seal you want the stock steel tube to deform when you swage the fitting on, not the fitting to deforn to the tube.

NPT because straight 8mm to -6AN was not available from Swagelok.

Female NPT because you want the stronger stainless in the female fitting and the weaker Aluminum AN fitting in the male fitting so female doesnt split.

Swagelok brand because I used a lot of their fittings at work on some high end industrial projects and it eas really reliable.

 

Just take a piece of fine sand paper and sand down the end of the steel tube.

 

Reviving this thread because I'm stupid and mixed up which fuel line is feed and return. I have both of them cut, but don't know which is which. Here is a diagram that I threw together. Can someone point me in the right direction?

 

From left to right in your picture: EVAP line (gas tank vent to charcoal canister), fuel return line, fuel supply line, rear brakes (prop valve to tee above rear subframe)