These plastic doodads are quickly replacing screws, and can be a PITA if broken since most people do not have extras in their toolbox. I'd like to keep an assortment on hand for my G2 and G3 Prii. Here is one source from Ebay for 9 mm holes, OEM part# 52161-20010 2000. 30 clips for $7 (shipping included) Please add other sources, other clips, and general information that might let this thread grow into a generally useful resource.
Funny you should ask, I'm wondering the same thing. My CT200h had two different sizes IIRC. In a couple of months It will be time for my first DIY oil replacement in our Prius Vagon. I think I'll get in the habit of measuring the clips if I cannot find the info any easier way. I have been rooting around the TIS for the past hour but have yet to find a summary sheet. In fact the page for the oil change just says 'clip' LOL
NAPA makes plastic rivets that are lower cost, higher quality, replacements for the Toyota fasteners. See my #7 post in my original thread below for details and pictures. Oil Change Door - Permanent Solution | PriusChat
I haven't measured the size of the NAPA rivets. The smaller NAPA one is exactly the same size as the smaller OEM rivet. The larger NAPA rivet may be slightly larger than the larger OEM, but it fits good.