Manifold: a conductor with multiple connection ports, generally made from a solid block of metal with internally drilled passageways to minimize the amount of piping required.

Manifold (lube systems): two or more injectors in the same mounting assembly.

Master divider valve (lube systems): in a series-progressive system, the first divider downstream from the pump; or the first divider value in a lubrication zone. Output is directed to secondary divider valves and/or lubricant points.

Measuring valve (lube systems): component that dispenses a measured amount of lubricant to a point of lubrication.

Mechanical seal: a dynamic interfacial spring-loaded mechanical device consisting of a stationary face component in a housing and a rotating face component on the shaft. Sealing takes place between the two flat sealing faces perpendicular to the shaft axis.

Mechanical stability: see shear stability.

Median life: approximately five times the L10 (rating) life of a bearing.

Micron: 10-6 m; one millionth of a meter.

Mineral oil: originally, the name given to petroleum because it occurs as a mineral, to distinguish it from oil obtained from animal and vegetable sources; more commonly, a lubricant made from petroleum.

Mineral seal oil: a cut between kerosene distillate and gas oil, widely used as a solvent or penetrating oil.

Mineral spirits: highly effective solvents derived from petroleum or coal (see petroleum spirits).

Mixed base crude/intermediate base crude: crude oil, neither predominantly paraffinic or napththenic in character, found in the Mid-Continent and other districts.

Mixed base grease: usually refers to a mixture of greases formulated with sodium and calcium soaps, though other combinations are available; though such compounding offers modest benefits, it is not sufficient to make them multipurpose greases.

Mixed film/imperfect film lubrication: lubrication in which the lubricant film is not continuous over the bearing area. Mixed film lubrication – lubrication accomplished by a combination of a viscous fluid compounded with boundary and/or extreme pressure additives. Example – worm gears.

Mobility: analogous to fluidity, the property of a lubricating grease that permits flow under pressure, as in centralized grease dispensing systems. Mobility is evaluated by low-temperature testing that simulates winter field conditions.

Mold oil: oil that ensures easy separation of a ceramic, glass, metal or other object from the mold in which it is cast (see form oil).

Molybdenum (“moly”) disulfide: often wrongly termed “molysulfide”; a dark powder used as a dry film lubricant in oxidizing atmospheres, at temperatures of up to 800°F, to reduce friction under boundary conditions. A natural material, moly disulfide is processed to remove abrasives, produced in micronic particle sizes and made available as a paste, an additive for greases, a dispersant in oil or a bonded dry-film coating.

Motor: technically, an electric motor; in hydraulics, a device that converts fluid power into rotary mechanical force (torque) and motion.

Motor oil/multi-grade oil: an engine oil that meets the requirements of more than one SAE viscosity grade classification, formulated with viscosity index (VI) improvers; “W” indicates winter grade.

MSDS: acronym for “Material Safety Data Sheet”, available for all raw materials and products; includes handling, storage and waste treatment practices recommended for safety.

Multi-purpose greases: greases with good mechanical shear stability, capable of operating throughout a wide temperature range and functioning in the presence of water, readily pumpable over long distances; such greases can be used in any type of bearing served by a centralized system (see lithium base grease and complex greases).

Multi-stage pump: centrifugal pumps with two or more impellers mounted on the same shaft; the discharge from one impeller is conducted to the suction eye of the next impeller, etc.

Multi-state compressor: compressor that directs air through a series of two or more cylinders during compression; “inter-cooling” denotes cooling as the air passes between cylinders.

Mutagenicity: tendency of a substance to cause genetic mutations under long term exposure.