T-duality defects (T-fects) are a class of codimension 2 supergravity solutions characterized by an O(2,2,Z) monodromy around the degeneration point. In this talk I will present a method to systematically determine and classify such local geometries. Furthermore, I will argue that physics near the core of these objects involves winding modes that are not captured by the supergravity approximation. Finally, I will discuss how these results can be (partially) captured by doubled space formalisms.