This is the SAS cable for the rear flex bay on the R740xd 12 Bay server. As noted in the part page for the 24 Bay cable, this cable is specific to the 12 bay chassis. A 24 bay cable looks similar but will not work due to differences in cable pinouts and backplane design. The proper cable for the 12 Bay server will be labeled A2 on one end. Match it up with A2 on the backplane.