fuel line inside measurement or outside

When talking about fuel lines people refer to them as the big one and small one. So, are the talking about the inside diameter or outside?
I just bought a carb kit and both lines seem to be the same size on the outside, but I think one of them is smaller on the inside. My eyesight stinks

I'm having a heck of a time replacing the line that goes to the fuel filter. I was able to get about 4 inches and thats it. Am using a hair dryer and WD40.
I had to cut the line when I removed it. My concern is stretching the line too tight.

Tks!!

Yes hand held fuel lines come in thin wall & thick wall sizes.
The thick wall gets hooked up to the filter & inlet while then thin wall goes on the return line.
use your packet of twist drills to work out which is which .
To get them through the tank / tank grommet use SILICON SPRAY not WD40 .
Poke a twist drill in the eng of the tube then use this to push the tube through the holes.
Never use heat on the tank or grommet as heat makes them sticky.

Wow. Thanks bertsmobile1. I greatly appreciate the help. I gotta quit watching Youtube.

I don't understand "Poke a twist drill in the eng of the tube then use this to push the tube through the holes". By twist drill, is that a drill bit? And there is no "pushing" the fuel line. I am able to grab on to it from inside the tank and I am trying to pull. I have pulled out about 2 inches, but the line stretched so far, I thought it would break. I have some Silicon Spray and will try that.

Also, if you get an email from me replying to your post, please let me know. I did not get an email when you replied to my post.


Aaron

Usual way to replace the fuel line is to poke a twist drill bit or any other close fitting wire into the tube .
Now push the tube with the wire inside it through the tank
helps if you remove the tank so you have easy access
Then use a thinner bit of wire to poke the drill out of the end of the fuel tube
Pull the tube back out the filler cap and fit the filter.