When the original Mac Pro was released in 2006, it included two side-by-side DVI-D connectors (Digital Visual Interface) on the back so two DVI displays could be connected at the same time.
Since the ports were close together, Apple shipped this DVI-D Male to DVI-D Female Cable Adapter in the event that the cable interface of the display was too wide to fit the connectors from both displays. The adapter’s function is to extend the port an extra six inches from the computer.
Sources: Apple (via B&H Photo Video), macofalltrades
