Rear housing ID help

Looking at references for 8 /3/4 rear end housings. I have a housing that measures 52 37/64 flange to flange. 3432647. I notice there is another housing that is 52 13/64 flange to flange. What is the difference and do I need to be aware when ordering parts such as bearings or even the axels?? Such a small difference, but it had to have been done for a reason???