This modular RJ12 connector is a 6 position, 6 conductor plug. It's typically terminated on 6 conductor flat cable. They are available as Singles, 10 Packs, 25 Packs and 50 packs.
These crystals are used to connect data driven devices such as TrolMaster controls.
Please see "Control Cable - 6 Wire - 26AWG Stranded - BLK - Flat" for the control cable that is best used for terminating in these crystal blocks.