These inline couplers connect two modular cables. They are wired straight through rather than crossed over. In other words, they are wired 1:1 (Pin 1 to Pin1, Pin 2 to Pin 2, etc). Each end of the adapter consists of a female connector and thus can be used to couple two male cables.
Several connector varieties are available: 4P4C (RJ-9), 6P6C (RJ11/RJ12/RJ14), 8P8C (RJ45), and 10P10C (RJ50). The options are pictured below.
