The type-B polarity MTP fiber uses a key-up connector on both ends of the cable. Often referred to as a 40G MTP cable, the type-B MTP cable is the second standard for polarity, and extremely versatile. 

This cable assembly can be used to plug directly between your 40G QSFP+ /100G QSFP28 optic transceivers, so it is commonly referred to as a QSFP/QSFP+ cable or direct attach 40GBASE-SR4/100GBASE-SR4.

 As you can see in the diagram, this cable has a "flipped" polarity and will result in a Pin 1 to Pin 12 relationship. This is extremely useful because 40G optics utilize parallel optics, meaning instead of alternating Tx and Rx in a duplex pattern, the port will look like the following diagram.