EXPLANATION:American Petroleum Institute (API) classification of cement:Class A: This type is intended for use when special properties are not required. Class B: This type is intended for use when conditions require moderate or high sulfate resistance.Class C: This type is intended for use when conditions require high early strength.Class G: This type is intended for use as a basic well cement. No additions other than calcium sulfate or water, or both, SHALL be blended with the clinker during the manufacture of Class G well cement.Class H: This type is the same as class G, class H has a coarser grind than class G which gives it better RETARDING properties for cementing deep wells.