First off, i want to say that i know nothing about cars and my Current 2007 Prius is my first car. In sweden where I live we need to switch tyres during the winter months. The previous owner for some unknown reason decided to use the original aluminium rims during the winter and a pair of other aluminium rims during the rest of the year. So after i went to Toyota for them to switch tyres i got to se the original rims for a first time. (Toyota also stores the spare tyres during the seasons) They have a bit of corrosion and dirt so they aren't pretty. But I was thinking, Shouldn't there be like a disc or something in the middle covering the bolts? If so, what's this part called? When I search for hub caps i get pictures of these plastic things that would cover the entire rim, if that rim wasn't an aluminium rim. This is a picture of the rim as I remember it, i can go down to the car and take a better picture later if needed.''
That rim does have full covering hubcap http://www.hubcaphaven.com/mm5/graphics/00000001/h61138_lg.jpg But you can also install center that only cover the small hole in the center from another Toyota rim.
If you want something inexpensive, try this: 2" Snap In Style Knockout Seal I bought 4 of these for my Prius v and it cost about $4 at Home Depot.
Yep, when we got the v earlier this year I took off the wheel covers to see a hole in the center. I thought, "cheapskates". I believe someone else suggested these on this forum, so off to Home Depot. Way cheaper and does the job.
If you want to pay more for the center piece, Toyota makes one with the Toyota emblem in the center. I used those when I took off my wheel covers.
you can also find a knockoff Toyota emblem center cap for about 20 bucks for all four. Toyota factory center caps can be pricey.. Toyota Corolla Center Cap | eBay
Thanks for the tips everyone! Now I know what to search for on eBay Usually I prefer all original parts, but this is purely decorative and to be used between October and April. The caps that mentioned from home depot i've only seen caps like that in white plastic that cover holes where wires otherwise would pop up out. But a knock off with an emblem would be nice.