A threaded rod hanger has quick lock plunger mechanism that includes plunger pieces within a tapered bore in a housing. The plunger pieces have tapered outer surfaces. A spring within the housing presses the plunger pieces toward the narrow end of the bore, with the spring located between the plunger pieces and a back plate that closes off part of a wide end of the tapered bore. The plunger pieces have internally threaded surfaces that engage threads on a threaded rod that is inserted into the bore, between the plunger pieces. Once the threaded rod has been inserted between the plunger pieces and released, the plunger pieces are pushed toward the narrow bore end. This causes the plunger pieces to press inward, automatically causing the internal plunger half threads to engage the external threads on the threaded rod.