I'm replacing my wheel bearings soon, so I ordered some timken replacements. I got them (ordered part# 512137 x2 for rears) and they're different! Here are some pics.

Here are the two and their differences.


Funny thing is, the only real difference are the locations of the smoothly-machined races. Height and inner diameters are exactly the same, give or take 0.0005", which is reasonably for bearing press-fit tolerances (had some calipers handy) and the bolt holes line up perfectly.

Here's the stamped number for the bearing on the left:


And here it is for the right:


So are these the same? The spindle goes through the bearing and is secured on the other side... so could I actually use both of these?

My first thought is As long as the mounting holes line up so you can bolt them in place and as long as both are the right size for the spindle to be pressed in then they should both work.
Although I have no idea why they sent you two different ones, it's obvious that they are not the same bearing. the first one that says Koyo is like the picture of the Timken replacement on rockauto.
Where did you order them from ?
I'd just be worried that the NTN is a lower quality bearing and you still paid the Timken price for it.

Yeah, that's kind of what I'm thinking... Subcontracted manufacturer or something? I ordered them off Amazon (Prime ftw) and I ordered them together. Timken 512137, Qty: 2. There's no reason they should be different. Came in the same Timken box (easily repackaged, sure), left from the same warehouse. I just don't get why they'd be different. I'm doing various other brake upgrades and all of my 'paired' parts are 100% the same, except these bearings.

I couldn't find any correlation between NTN and Timken, other than an incident in the 80s where NTN was selling components too cheaply and Timken complained, saying they were undercutting the competition. Court found them guilty and they had to pay some relatively small fees.
Other than that, I've actually found that many forums/message boards hold NTN (and SKF) in higher regard than Timken!

I also made sure that the NTN bearing I received is the correct rear bearing for the 94-99 Celica FWD application.

I'll probably be fine with this bearing...

Ah yea, reboxed parts. Love that. Order two ball joints and get one that's a Moog in a non Moog box and the other is some wimpy looking crap with no grease fitting, or order two sway bar links and one comes beefy and strong, the other one looks like the paint was still drying when it was shoved in the box in China. Same numbers on the boxes.