If you are trying to link several line cords together or extending existing modular cable runs Cables To Go s In-line Modular Couplers can help you make the right connection. The in-line coupler provides a female-to-female feed-through connection for easy cable hook-up. Connectors: One RJ-12 Female to One RJ-12 Female. Type: Straight-Thru RJ-12. Designed For: Data/Voice Applications. Use: Extends the length of two modular cables.