I’ve been struggling with these Apex rear axles. They require OEM 370Z axles, no aftermarket and not G37 ones. I ordered used ones on eBay, which they recommend, one wasn’t OEM because it had 6 bearings, OEM has 8. So I think I have correct axles and after struggling for a while with the side that has the internal snap ring I looked at the donor axle and the groove is deeper than the new ones. So not sure if new ones have an issue, or if I still don’t have the OEM 370Z axles. Sent Apex and email, we’ll see what they say.