In this paper we study quantitative as well as qualitative properties of Fork/Join queueing networks with blocking (FJQN/B's). Specifically, we prove theorems regarding the equivalence of the behavior of a FJQN/B and that of its duals of a circuit-free FJQN/B, and a strongly connected marked graph. In addition, we obtain general conditions that must be satisfied by the service times to guarantee the existence of a long term throughput and its independence on the initial configuration. We also establish conditions under which the reverse of a FJQN/B has the same throughput as the original network. Last, by combining the equivalence results for duals and the reversibility results, we establish a symmetry property for the throughput of a FJQN/B.