Like many of us, I’ve searched high and low for options on how to get more standard lines onto my 1969 gas tank. I picked up one of the 1/4 barb adapters and, to my surprise, found that my tank had been modified by some enterprising PO to have a female fitting instead of the standard male. I gave up on the old tank and bought a new one from Toyota, but I still wanted a better fuel line setup. After a few false starts, I made the following discoveries (at least discoveries to me)

1. M13x1.5 DOES actually exist in a fairly common form. Oil pan drain plug re-thread kits!
2. 8AN fittings are large enough to fit the entire fuel line male fitting inside.
3. The adapters I have found look to be thread sealed, so it doesn’t seem like I need to worry about matching faces on the fittings
4. pipe dope hides sins.

So here we go.

If you Amazon “M13x1.5” you’ll find a bunch of oil pan drain plug re-thread kits. We really just need the tap, but this is usually the cheapest way to get them.
Next you need a 12.2 mm drill bit, also readily available on Amazon.
Lastly, an 8AN plug adapter. It’s important that you get the plug that actually has the AN flair on the end and not just the flat bottom plugs.

Using a smaller drill bit, make a pilot hole in the center of the AN plug. You can do this from the AN side and you’ll find that the center is probably already got a nice little dent to help you get started.

After drilling your pilot hole, flip the fitting over and enlarge the hole with the 12.2mm drill bit. It’s VERY important to NOT go all the way through the fitting, you’ll mess up the AN seat. All you need is around 5/8 or so of depth to be able to get the tap in there and past the pilot threads. Remember, you can always drill deeper later.

Now tap out about 1/2 inch worth of threads using the m13x1.5 tap. If you bought the kit that has the plugs with the tap, you can use a plug to help get those last few threads cut if you need to. The AN fittings are aluminum and the plugs are steel.

Do a couple of test fits to make sure the plug seats nicely. You will likely want to use some sort of pipe sealing tape or dope just to make certain you won’t have any leaks, but I believe the old fittings were thread sealed also so nothing new there.

You can now fit any 8AN fittings you want onto your tank. Do keep in mind that when you go to tighten the AN fitting onto the tank, you need to use two wrenches. That poor little fitting on the tank isn’t going to appreciate 150lbs of torque bearing down on it.