A Note About USOC Number Suffixes

RJ (Registered Jack) numbers end with a letter that indicated the wiring or mounting method:

• "C" identifies a surface or flush-mounted jack.
• "W" identifies a wall-mounted jack.
• "X" identifies a complex multi-line or series type jack.

This webspace contains descriptions of Universal Service Order Codes (USOC) for connecting telephone instruments and related equipment to telephone lines via standard telecommunications jacks, based on Part 68, Subpart F, Section 68.502 of FCC regulations, and as described by the T1E1.3 Working Group on Connectors and Wiring Arrangements.

USOC Codes were developed years ago by the Bell operating companies to identify service or equipment under tariff.