Automotive gear lubricants, similar to engine oils, are classified by the API in terms of the performance required by a particular application. As in the case of engine oils, these classifications do not define or reflect oil viscosity. To completely specify a gear lubricant, both the API service designation and the SAE viscosity grade are required. Axle and transmission lubricant viscosities are defined separately in SAE J306 recommended practice. Multigrade lubricants are normally used and each viscosity grade has distinct criteria for low and high-temperature performance.