Spindles are rotary components that often work in groups in industrial machines - these components, moving at both high and low speeds, are subject to high pressures and intense working conditions, requiring them to have specific lubricants. Some spindles call for an ISO VG 15 oil. Circumstantially, pneumatic or air tools may benefit from the same or similar weights and types of lubricant.
The midpoint kinematic viscosity is derived from an average of measured kinematic viscosities. This number is found by taking the maximum and minimum viscosities and finding the average. This number also represents the ISO VG number - in this case, ISO VG 15.