A modular flooring assembly for heavy-duty applications is presented. It is made of a plurality of interlockable mat units, each mat having a plurality of edges with at least one edge having a connector in the plane of the mat unit. Each connector is made of a plurality of alternating teeth and grooves respectively adapted to engage the grooves and the teeth of another mat unit. Each groove has a first bevel with respect to the plane extending along its back wall and a rear portion of its corresponding side walls. Each tooth has a second bevel with respect to the plane extending along its front wall and a front portion of its corresponding side walls. The first and the second bevels are complementary and each side wall form a twist transition between the first and second bevels.