Polyalphaolefins (PAOs) are hydrocarbon oils that are synthesized by polymerizing α-olefins. PAOs are API Group IV base oils. They are noted for their chemical purity, consistent molecular weight distribution, and high viscosity index, and they can be used over a wide range of temperatures.

An arbitrary standard measure of consistency (hardness) based on ASTM D217 (ISO 2137). The softer the consistency, the higher the penetration number.

The ASTM Definitions are:

Penetration – The depth that a standard cone penetrates a sample of lubricating grease under prescribed conditions of cone weight, time and temperature. Penetration is measured in tenths of a millimeter, sometimes abbreviated dmm.
Undisturbed Penetration – The penetration of a sample of lubricating grease that has not been stirred or disturbed measured at 25°C (77°F).
Unworked Penetration – The penetration at 25°C (77°F) of a sample of lubricating grease that has received only minimum disturbance in transferring to a grease worker cup or dimensionally equivalent container.
Worked Penetration – The penetration at 25°C (77°F) of a sample of lubricating grease immediately after it has been subjected to 60 double strokes in a standard grease worker.
Prolonged Worked Penetration – The penetration at 25°C (77°F) of a sample of lubricating grease that has been subjected to more than 60 double strokes in a standard grease worker at a temperature of 15°-30°C (59°-86°F). Typical numbers of double strokes used for prolonged working are 10,000 and 100,000. After the prescribed number of double strokes, the sample is brought to 25°C (77°F), and worked an additional 60 double strokes, and penetration is then measured without delay.
Block Penetration – The penetration at 25°C (77°F) of a sample of lubricating grease that is sufficiently hard to hold its shape, determined on the freshly prepared face of a cube cut from a block of grease.

See Cone Penetrometer

Poly(internal olefins) (PIOs) are hydrocarbon oils that are synthesized by dehydrochlorination or chlorination of linear paraffins. They have high viscosity indices and low pour points, and they are used in engine oils, compressor lubricants, and other applications.