An I/O device includes an I/O base, at least two I/O modules supported on the I/O base, and a duplex terminal block assembly supported on the I/O base. The at least two I/O modules include a first I/O module and a second I/O module coupled to the duplex terminal block assembly in parallel. The duplex terminal block assembly can include connectors for connecting to a field device. The duplex terminal block assembly can include conductive structures for coupling the connectors with each of the first and second I/O modules. The duplex terminal block can be installed in a pair of ports in an I/O base to connect two I/O modules in parallel.