I thought the OP was implying the replacements he got were smaller than the OEM rear calipers.Good timing, I happen to be replacing my rears today too. The rears are much smaller than the fronts. They are only about half the size as the ones on the front. Really, they look like toys in comparison.
They are somewhat smaller. Thinner too, at around 10mm nominal vs 12mm nominal in the front. Both have the same service limit at 1mm. And naturally, with the rear brake bias, the rear pads wear quicker than the front pads. I changed my rear pads out in the mid-70k range while the fronts were about mid-point in wear. I figure when I change out the fronts it will be time to replace the rear pads again... or close enough.Good timing, I happen to be replacing my rears today too. The rears are much smaller than the fronts. They are only about half the size as the ones on the front. Really, they look like toys in comparison.
Rockauto and just about every other aftermarket supplier sells REBUILT / REMANUFACTURED OEM brake calipers and brackets. There is a core charge that you get back when you return your old parts. The quality of the rebuild process my vary but the actual caliper body and bracket body is an OEM part. They don't typically sell new aftermarket calipers. . . There is no good reason that they are the incorrect size other than some sort of labeling / cataloging F'up. . .
With that much difference, I would likely go with a remaned as well. The quality of a rebuilt part is important, though I imagine they are mostly reconditioned similarly. Not that many parts to it anyway.For instance: a new OEM caliper and bracket is $176 from Bernardi. An aftermarket rebuilt caliper and bracket is <$50 Both are OEM main bodies while the rebuilt caliper will have aftermarket pistons, slide pins and various rubber bits.