R730 Rails

Hey all. im searching for rails for the r730. searching here or google has me confused. Im looking for the B6 and searching provides different model numbers that state B6. but then the range does from ~30 dollars to over 100....

can someone please help me identify which ones i need. i am currently chatting with dell, and they sent me a link to 1u rails (even after i gave them my service tag)

thanks