I just told you (a couple of posts up), it's a PCV hose, made of rubber, about a foot long with a 90 degree bend in it. I know the hose, but didn't remember whether or not the ends were the same size. Only hot air and perhaps some oil (in vapor form) should be going through it. It's purpose is to connect the crankcase to the intake manifold to alleviate block pressure and keep a vacuum on the block itself and thus decreasing oil blow by at the piston rings, as well as other functions. Search "PCV system" on here, alot has been written about it.
EDIT: Ok, I was NOT correct about the ends being the same size. Here is the item you want, a place to get it, and an easy link to click. Click Here This part MAY be available from your local Nissan dealership, (and may cost less).