A universal cable hanger or clamp that can accommodate a variety of cable sizes, and can be mounted on a variety of structures in a various ways. The hanger includes a fixed block with a movable block, where the fixed block can be clamped or attached to a fixed structure, and includes a pair of partially open curved sections adapted to receive and hold cables of various sizes. The movable block includes two curved or V-shaped or U-shaped arms that correspond to the partially open curved sections. As the movable block is inserted into the fixed block, the arms close off the curved space, in whole or in part, to grip and hold a cable in the space. Two posts on the movable block engage indentations in slots on the fixed block, thereby providing a curved space of fixed size corresponding to different cable sizes. Multiple hangers can be stacked.