The Stovebolt Site Forums The Shop Area General Truck Talk NPT Threads on Flared Tubing?

I just received my new stainless steel fuel line from Inline Tubing. It's 5/16" O.D. with flared ends and the NPT screw fittings on each end. Can someone tell me what the correct thread identity is on this fitting? I need to know so I can purchase the correct brass female flared tube fittings with a barbed hose connection just after the gas tank. The brass barbed hose fittings are to connect a short rubber gas line tube to eliminate vibration in the gas line between the tank and the main fuel line running to the fuel pump. The connection is supposed to be for flared tubing not compression such as a Swag lock.

NPT means national pipe taper. The fittings on your gas line are likely 1/8 or 1/4 NPT The thread pitch is 27 threads per inch and they are tapered in order to make a seal as the fitting is tightened. I suspect your fittings are 1/8 pipe. your barbed fitting should have 1/8th pipe threads on it where it screws into the tank. I think 1/4 threads would be too big. Without seeing the hole in the tank where the fitting goes I am only guessing. I hope this helps. You could buy both sizes and use the one that fits. Good luck.


Weeds

If you are asking about the end of the tubing you purchased: I don't believe the threads on the tube nut are NPT. They are straight SAE 1/2-20. You are not sealing a pipe thread seal. You are clamping a flare into it's seat.
Furthermore, you don't need a barbed fitting. Just slide the nut back, slide the hose on and clamp. The flare is your barb.
If you really want a fitting, take the line to the store and try fittings to find the correct thread.

If you are asking about what to do at the tank outlet, need more info. Tank probably has 3/8 NPT female bung.

bartamos,

You are correct about the straight SAE 1/2-20 threads! I just went out to the garage and found a 1/2-20 hex nut. Bingo! You are also correct in how a flared tube seals. I do want to get a couple of barbed brass hose fittings that accept a flared tube fitting, so now at least you helped me figure out the correct type of threads I need to specify. There is a Fastenal here in town and I can order these parts from them. Ordered a new shut off gas tank valve and hope it fits. Hard to tell right now about the NPT threads in the tank outlet, but I think your guess is probably correct.

Want to solve all gasoline leaking issues! Right now its the tank valve that is giving me issues.

The extra fitting, instead of just slipping on the hose, is an extra leak point. Also there is no need for a shut off valve. If you ever need to "shut off" the tank outlet you can pinch the hose with vice grips. That valve is also an additional leak path. You can just install a barb fitting into the outlet.

Just get a hose barb fitting in the correct tubing size with a NPT male thread correct to screw into the tank. Ebay is full of them- - - -no point in paying an outrageous markup at Fastenal!
Jerry

I was thinking that too. Any FLAPS or hardware store will have those fittings. Fastenal probably won't sell onesies or twosies.

Ya think so? I spent all day looking for a couple of 1/4" NPT-1/4" hose fittings a couple of weeks ago to plumb the gas system on my new MIG welder with, and nobody in town had them. I finally found them in plastic at an oldtime hardware store on the town square! All the FLAPS have just about stopped stocking brass fittings of any sort.
Jerry

It's different in Phoenix Arizona than in Dellrose, TN. O'Reilly's has them, Ace has them, Napa has them and there are hundreds of other stores. Home Depot, Lowes......
I do realize that in small towns, mail order is the way to go on even fittings. I use mail order (internet) all the time for other items. Did not notice poster's town and possible lack of stores.
Signed: "Big City Boy"

All things considered, I'll take my hundred acres in the boondocks over a little shopping convenience any day. Try target practicing out your back door one of these days, or building an addition onto your shop without jumping through a bunch of hoops and bribing a few politicians first!

BTW, I tried Auto Zone, O'Reilly's, Advance Auto Parts, and two "modern" hardware stores first! We're not quite as primitive as the Beverly Hillbillies here. I've even got electricity, running water, and indoor plumbing!
Jerry