For instance RG-6, RG-58, RG-59 and RG-173? Also do the numbers have a specific meaning (like referring to a part of the specification)? Is there a document that lists all RG-* cables with their specifications?
A series of standard types of coaxial cable were specified for military uses, in the form "RG-#" or "RG-#/U". They date from World War II and were listed in MIL-HDBK-216 published in 1962. These designations are now obsolete. The RG designation stands for Radio Guide;
From The obvious place
A simple wikipedia search gave this: http://en.wikipedia.org/wiki/RG-59
Usually even numbered cables (RG-58, RG-316 etc) have 50Ohm impedance and odd numbered have 75Ohm