Rotary shaft seals sit between rotating and stationary parts on a shaft to retain lubricants. Rotary shaft oil seals include a garter spring that presses the sealing lip against the shaft for a tighter seal to retain oil. Rotary shaft grease seals have a slightly looser fit to the shaft, without a garter spring, to reduce friction and still retain grease. Spring-energized seals, also known as spring-loaded seals, have an internal spring to ensure the seal maintains its shape to retain lubricants and seal out contaminants. Wear sleeves provide a smooth, concentric surface so that the shaft can properly seal to a component to retain lubricants and keep out contaminants.