How do you measure brake line, heater hose etc?

[v7guy]

I've been intrested in replacing alot of the plumbing in the car and do not know how brake line, heater hose, fuel line etc are measured. Is it measured by inside diameter, outside diameter or is there another way. I would presume it's just a measure of the cross section but I'm looking for confirmation before I start ordering things.

[Matt@RFR]

Inside diameter.

[CarlC]

Hard brake and fuel lines are measured by the O.D. and wall thickness.

Flexible hoses are measured by their bore size, and the hose type is dictated by the application.

[Matt@RFR]

And all AN sizes are measured by ID.

[CarlC]

Matt,

AN hardline is still measured by O.D. (nuts, sleeves, etc.)

[Matt@RFR]

Damn, you're absolutely right. I remembered it as ID for some reason. Sorry about that.