This is correct, the "bolt" exclusion from top of one unit's case fit directly into the "socket" of another unit's bottom plate.
Excellent. That will make for one very practical setup - just stack all your units on top of each other. There might be minor differences in temps as the one at the bottom will draw in relatively cooler air, but the differences should be minor.
By the way BitSyncom, I must say I like the case design and appreciate the fact that it's solid aluminium - it is very sexy in an raw industrial design sort of way
Now excuse me while I go and rub my hands all over it...
now don't go and lose $500,000 worth of BTC this time.