The most common grades of CATV cable used in homes today are RG59 and RG6 (aka RG56).

RG59 was the standard for home wiring many years ago, but is generally problematic today. RG59 is a lower grade of coaxial cable, consisting of a small center conductor, a small insulating dielectric, and typically, a single outer shield.

RG6 is the standard today and has a larger center conductor, a dual or quad shield, and a much larger insulating dielectric, thus ensuring more bandwidth and a lower frequency loss per foot.

RG11 is higher quality than RG6, but also much thicker and harder to work with. It is usually used for longer cable runs (over 150 feet) because it loses signal more slowly. I do not know of any stores that carry RG11/F11 cable.

There are several other grades, but they are uncommon and beyond the scope of this FAQ.