[Al Skierkiewicz]

Nick,
There are two grey parts that were provided for this terminal block. The three blocks with the screws are the devices that tie the blocks to the rail. I recommend you use all three, one at each end and one in the middle, to keep the terminals snug. The grey spacers (thin grey parts) are meant for insulation between adjacent blocks. Although there should be no chance of electrical problems if you don't use the spacer, they will provide additional mechanical isolation betweent the adjacent blocks.