Fuel tank - "Filler Collar" help

[2.5T_/<ouki]

It appears that my gas tanks "filler collar" is missing! I haven't run the car yet since I've purchased it as I've been removing all the parts, cleaning, and upgrading. What does this "filler collar" do? Is it really needed? It's almost like it regulates how fast the fuel drops inside of the tank? I don't have this part anywhere and I can't find it anywhere online. FSM #10

http://i65.tinypic.com/azdx83.jpg

http://i63.tinypic.com/2w66hhk.jpg

[derass]

Is it really needed?

If Nissan spent millions of dollars including it in their design, you can be sure it has a purpose.

[2.5T_/<ouki]

Apparently, the little collar is only there in case the car ever flipped over, the collar would stop the gas from spilling out.