This paper introduces the concept of the trans-rotary magnetic gear (TROMAG). The TROMAG is a magnetic device consisting of a rotor and a translator with an air gap in between, capable of converting linear motion to rotation, and vice versa, and doing the gearing action at the same time. Although its structure suggests that the TROMAG is simply the magnetic dual to the mechanical lead-screw, the authors show that the concept could also be derived from the elementary magnet arrays. The paper tries to establish an analogy between the TROMAG and the ordinary electrical machines with respect to the number of poles and the stack length, thus providing a deeper insight into the device operation. Three-dimensional (3-D) finite element analysis (FEA) is deployed to obtain the torque and force characteristics. Furthermore, it is shown that in addition to the permanent magnet (PM) TROMAG, developing the reluctance and the induction TROMAG is possible as well, but at a lower force density.