The (.1) is because the cars hub is 64mm for the rear, and 70 mm for the front. So, the (.1) is for the rims center bore which needs to be just a little bit larger than the cars hub in order to fit. To tell you the truth, I've used aftermarket hub centric rings with aftermarket rims that came with 70.03mm hub rings as well as those that came with 70.1mm rings for the front and similar for the 64mm rear. The 0.3mm rings are a tight fit and if you have a little rust on the hub it can get stuck real easy. The .1 seems to fit well and slide on and off fairly easy, but still not too large and to loose the hub centric fit.