Casing string:

The entire length of all the joints of casing run in a well.

Most casing joints are manufactured to specifications established by api, although non-api specification casing is available for special situations.

Casing manufactured to api specifications is available in three length ranges.

a joint of range 1 casing is 16 to 25 feet long; a joint of range 2 casing is 25 to 34 feet long; and a joint of range 3 casing is 34 to 48 feet long.

The outside diameter of a joint of api casing ranges from 4 1/2 to 20 inches.