LB stands for Logic Board. On all standard Macbook Pro's there is a cable running from the standard hard drive bay to the Logic Board (the Logic Board is the Motherboard, main component in any computer). This cables fail on many model MBPs. If you put a drive of any type, SSD or standard drive, in the Main Bay and the OS does not see it then the cable has failed. Or the SATA controller or socket that cable is connect to has failed which is unlikely.
Oops - my bad - I had set the ifixit page to my own model!
Yes, if you've a 13" early 2011, that's the cable you will need.
Sorry for my misdirection!