The RG numbering system of coaxial cable (coax) refers to the fact that the RF (Radio Frequency) signal is guided down the center conductor of the cable system. The RG numbering system dates to WWII United States military specifications and has no real contemporary significance other than type designators. Each RG number does, however, specify impedance, core conductor gauge (AWG) and type, outside diameter (OD), and other physical attributes of the cable. Table R-2 compares example coaxial cables. See also coaxial cable.

Table R-2: Coaxial Cable Types

RG Number	Center Wire Gauge	Impedance	Outside Diameter (OD)	Core Type	Example Applications
RG-6/U	18 AWG	75 ohms	.332 in.	Solid	CATV, cable modems, DBS TV
RG-8/U	10 AWG	50 ohms	.405 in.	Solid	10Base5 Ethernet, Ham radio
RG-58/U	20 AWG	53.5 ohms	.116 in.	Solid	10Base2 Ethernet, Ham radio
RG-58C/U	20 AWG	50 ohms	116 in.	Solid	RG-58A/U Military Spec
RG-58A/U	20 AWG	50 ohms	116 in.	Stranded	10Base2 Ethernet, CATV
RG-59/U	20 AWG	75 ohms	146 in.	Solid	Ham Radio, CCTV
RG-62/U	22 AWG	93 ohms	.146 in.	Solid	ARCnet, IBM cabling system