A better understanding of flux behavior within specific regions of a transformer core can lead to improved core design and magnetic efficiency. Flux paths and the flux transfer mechanisms have been determined for two practical T joints of different designs employed in two similar three-phase three limbed transformer cores. Each core was energized at three different core flux densities. The instantaneous flux density patterns both parallel to and perpendicular to the rolling plane of the laminations are presented in graphical and vectorial forms for both types of T joints. By "freezing" the continually changing flux pattern within a T joint, it was possible to trace individual flux paths through the joint and to determine the basic flux transfer mechanism between adjacent laminations. Flux behavior within the joints shows that while its path is dependent on both T joint design and core flux density, the basic flux transfer mechanism remains unchanged in both T joints and at all core flux densities.