An adapter for mounting cable hangers to a mounting structure includes: a plurality of mounting panels including a mounting hole, the mounting panels attached to each other at edges thereof and being disposed at an angle relative to its adjacent mounting panels; two base segments, each attached to the edge of an endmost one of the mounting panels and extending therefrom toward each other, the base segments and the mounting panels defining an interior region of the adapter; and first and second locking arms, each locking arm extending from an end of one of the base segments and including a locking feature, the first locking arm extending generally parallel to the second locking arm and defining a gap therebetween; and a reinforcement unit including a flexible arm and a stop configured to fit within the gap and inhibit deflection of the locking arms.