From what I learned way back when, the 4203 bearing is fairly hard to find, and was used mainly in England for Euro-household appliance applications. The double row SKF 3203 is by far the highest-technology, most modern, best quality bearing, with much higher axial load capacity, as compared to the 6203, 4203, and 5203. MUZBOMB, another technical answer to your question is some machines require drive shaft machining, to get rid of axial loading, no matter what bearing you choose. Best of luck!