RJ-41 M and RJ-45M: Provide a multiple-mounting arrangement for mounting a number of RJ-41S or RJ-45S Single-Line Universal or Programmed data jacks. The tele- phone companies will terminate USOCs, RJ-41 M, and RJ-45M with RKM2X (which is the USOC equivalent for a mounting arrangement) and the appropriate number of RJ-41 S or RJ-45S single-line data jacks as required by the user. The mounting arrangement will accommodate up to 16 single-line data jacks. In effect, this arrangement provides the features of a patch panel. The user has complete flexibility in patching the color and plug from any modem to any line. The arrangement can be mounted on a wall or on 19- or 23-inch relay racks.

RJ-41 S: Is a single-line universal data jack normally associated with fixed-loss loop (FLL) or programmed (P) modems. A switch, accessible to the user, is provided to select FLL to P type of operation. (FLL equipment transmits at -4 dB with respect to one milliwatt, and a pad is included in the data jack so that pad loss plus loop loss is nominally 8 dB. Programmed modems adjust their output power in accordance with a programming resistor in the data jack. By these means, signals from either FLL or P types of registered modems will arrive at the local telephone company central office at a nominal -12 dB with respect to one milliwatt for optimum data transmission.) A sliding cover is provided to keep dirt and dust from entering the jack when it's not in use. The FLL /P switch selects the desired method of operation. Two matted surfaces are provided on the housing of the jack for the telephone company installer

RJ-45S: Is a single-line data jack normally associated with programmed (P) modems. This jack is the same as the universal data jack RJ-41 S described above, except that the pad for fixed loss loop (FLL) equipment and the switch to select FLL or P type of operation are omitted. Its appearance is the same as RJ-41 S except that RJ-45S does not have the FLL /P switch. Both jacks provide bridged connections to the tip and ring of a telephone line and provide mode-indication leads for use with exclusion key telephone sets when required. The exclusion key telephone set requires a series jack RJ-36X as its normal means of connection.

RJ-48S: Normally associated with DDS services from the telephone company this jack is used with DDS CSU/DSUs.

RJ-48C: Normally associated with a DSX-1 Interface for a T1 circuit this jack is used with T1 channel banks, T1 CSU/DSUs.

RJ-48X: special wiring