The Model 121 is a 1/4" stereo 2-conductor cable mount jack with solder contacts and cable clamp.
Extension Jax® jacks are connected to the end of a cable. Jacks mate with standard commercial phone plugs, and have a sturdy cable clamp strain relief, knurled shielded or molded black plastic handles, and a screw type solder terminal. All internal parts are interlocked.