Spherical roller bearings are self-aligning, double-row, combination radial and thrust bearings. They use a spherical or crowned roller as the rolling element. The outer ring contains a spherical race which allows for some misalignment of the shaft and housing. Spherical roller bearings are unequalled in their capacity for high loads and tolerance to shock loads, but have limited speed capabilities. They perform consistently, even under conditions of extreme speed, application specific stress, and marginal lubrication. The cage of a spherical roller bearing provides high dimensional accuracy and functionality. According to some estimates, spherical roller bearings have twice the running life of conventional bearings.