They sell OEM spec parts. That doesn’t necessarily mean factory parts (although they do carry them in some cases) it simply means the parts were, (supposedly) made for factory specs. This is why there are so many options for each part. You will notice a few different grade parts from the same manufacturer in many cases, especially suspension and u joints.

.that said, I’ve had very good luck with them. A couple of items were mis listed .but really not their fault. The numbers were exactly what the manufacturer had listed in their catalogs.

Some of the cheaper parts are AutoZone grade, as in wolk great in a beater car or one you are planning on getting rid of. Otherwise, stick with known brands (although lately, I’ve got a rash of bumn GMB parts after installing them for years without issues, again, not rock autos fault).