Socket Size for Wheel Lug Nuts?

I think it's item 8 here:

Wheels for 2010 Toyota Prius | Toyota Parts

Those are for the 17" rims, but as far as I know the center cap will also fit the 15". I'll actually be able to check that in a few weeks: we have 17" OEM, and I have some 15" PIP rims I'm going to check fit, before putting on snows.

If you take that part number (42603-52110) and check on Ebay you should be able to find cheaper. The image on that above site for the centre cap appears to be messed up btw, but if you google that part number you see it is the alloy rim centre cap.

 

I was about to put those oem nutz on a steel but it look weird and when i realized those washers on the move

 

Bit misunderstanding, remember that steel cover on old cars, you have to use screwdriver and hammer to took it off and big screw(32) appeared...

 

The result