DD11-C backplane
From Computer History Wiki
The DD11-C backplane is a 4-slot MUD backplane system unit. It was normally installed in a BA11 mounting box.
There are two versions, the BA11-CF and BA11-CK, intended for use in the BA11-F Mounting Box and BA11-K mounting box, respectively; they differ basically only in the length of the power harness, although the two provide +5VB (battery backup) on different pins of the DEC power distribution connectors.