I'm looking to see what size fuel sending unit for 340-6 please? 3/8 or 5/16?
Need to replace the tank/sending unit. The line on there currently, the size is unreadable. Again this is for the sending unit from the tank.

I would think it would match the feed line to carb. See if you can measure the feed line and get that size.

I think the fuel line was consistent rear to front on all Mopars of that era, judging from the ones I've worked on.
Try to get a measurement by whatever method:
1. Calipers/"dial indicator"
2. Reading a hose if any of the printing is visible
3. Slit a short length of 5/16 & 3/8 hose, slip it over the line and observe proper fit.

Stock is 5/16" which works fine even in higher HP applications.

Likely 5/16 if OE but you could slip an open ended 5/16 wrench on the steel nipple coming out of it. New sending units are the worst of the worst for reading off & see if you can pull up prior threads regarding this for some good companies to deal with or just scroll back a few days to a week (I think there was a recent comprehensive thread on this awhile back).

Less restriction on the suction side of the pump is always a plus. Go 3/8" and you will have room to grown with basically no down side other than any price difference and maybe a tiny but more attention to detail during installation.

I know when I converted to EFI the instructions required 3/8" feed line and you reused the original 5/16" line as the return to the tank.

X2

Thanks everyone!

Thank you Scott! I'm gonna go with 5/16