Abstract: A section of heat treated solid steel rod receives a phosphate solution treatment and is inserted into a blind cavity of a first die member within a cold forging press. A punch is forced axially into the rod section in successive steps to cold-forge a first bore and a tubular first end portion of a coupler body. A second end portion of the coupler body is also cold-forged in successive steps after treatments and is either reduced in diameter to receive external threads or is formed with a second bore. Each of the first and second bores receives an end portion of a concrete reinforcing bar after which the tubular end portion of body is compressed or swaged inwardly to secure the body to the reinforcing bar. The second bore may also be machined with internal threads for receiving the external threads on another coupler.