In most operating environments though, the requirement is twofold: to keep the lubricant in the bearing, while stopping moisture, debris and other contaminants from getting in. Of course, while the shields are providing their protective functions, the ball bearing is spinning, often at high speed. If its operating life is to be maximized, one factor that needs to be considered is the frictional effect of the shield on the bearing starting and running torques. Essentially, shields are non-contact metallic (carbon or stainless steel) devices which allow high-speed operation but offer limited protection against the ingress of moisture and dirt. Shields have no contact with the bearing inner ring, hence their low torque qualities. Shields are better than seals at resisting damage from solid airborne contaminants, such as small flying stones. Bearings with shields are primarily intended for applications where the inner ring rotates. Shields are fitted in the outer ring and do not make contact with the inner ring, but form a narrow gap with it. Depending on the bearing design, series and size, MANU supplies shields in different designs.