To the OP, just curious why you want to know. Also, any dealership parts department can sell you the Toyota washer for about $1. Buy one and measure it?
If I buy the Toyota 0W-20 oil and filter at the dealership, they toss in the plug gasket gratis (woo-hoo!!!)
I'm pretty sure the engine oil drain bolt requires 14 mm wrench, going from memory, from last time. That very likely equals 10 mm bolt (at the threads) meaning Rude person's (up the page) is right, saying the washer is 12 ID and 20 OD. My 2 cents, when it's oil change I go to the Toyota parts counter and get: one washer, 4 liters oil (occasionally 5, since it can take a tad over 4) and a filter element. It's all on one invoice, helps with the paper trail, at least I like to think so. The washers they sell at Toyota (and Honda fwiw) these days have bonded plastic liners, and in my experience these can be trouble prone. With a Honda one in particular, even though I know I've torqued the bolt, often the next time I get to it it seems quite loose. And the plasticky washers can be a pain to get off the bolts.
if anybody would like to know size they are 12mm hole x 20mm outer and 1,5mm depth and they fit very nice . you can buy them in packs of 10 for £1.59 /// Toyota would want that for 1 every penny helps
Sump plug washers.......... Get a Copper washer 12mm Diameter. The engineering part is you want a seal which won't loosen or leak. A copper washer will compress with less torque than the torque required to sufficiently tighten the bolt/Sump plug. You can get 100 for £2. Reason I say Copper washer is they use them as air tight seals diesel injectors for a reason....
