If you go to your Nissan parts counter, the nice parts counterman should be able to show you what parts are available in the parts book. Then he can tell you what you can buy & you can chose which part[s] that you want right there on the spot.
You can also learn what the name of the 'thingy' is by pointing to it in the illustration.

This way you get your questions answered quickly & you can order the parts immediately.