Duplex cockingi is a moth of the Micronoctuidae family. It is known from south-western Queensland and the northern part of New South Wales. The wingspan is 11–12 mm. The forewing is long and broad. The subterminal area is grey. The crosslines are all present and black. The terminal line is marked by dense black interneural spots. The hindwing is light grey, without a discal spot and the underside of the forewing is blackish grey, while the underside of the hindwing is grey, with an indistinct discal spot.