The Bearing Buddy 42201 II Bearing Protection and Lubricant keeps water and dirt out of the hub while internal pressure is always maintained at 3-PSI. The 42201 features a high quality, stainless steel construction for its internal parts and a triple chrome-plated barrel. This is the ultimate bearing protector with the added feature of "Auto Check: Visual Lubricant and Pressure Indicator." This updated version of Bearing Buddy has a spring loaded piston behind the Auto Check ring that pushes against the grease which generates pressure inside the hub to keep water out. If the lubricant is low, the blue Auto Check ring will recede until it is flush with the steel-retaining ring. Add a small amount of grease to move the blue ring outward about 1/8 -inch. Its that simple!