Oil seals have a flexible lip that rubs against a shaft or housing to prevent the leakage or contamination of fluids and debris. For proper installation, the seal lip should point towards the lubrication being contained. Some oil seals have a spring to help keep the lip in contact with the shaft. The sealing orientation and direction is important to consider for oil seals and grease seals. Rod seals are radial seals. The seal is press-fit into a housing bore with the sealing lip contacting the shaft. Piston seals are radial seals. These seals are primarily used for rotary applications only. V-ring seals are all rubber seals used primarily to exclude dirt and other contaminants. V-rings stretch over a shaft and seal against the side of a housing or other machine component. There are many different styles of clearance, or labyrinth seals.