MACHINE FINISH: Operation of turning or cutting an amount of stock from the surface of metal to produce a finished surface.

MAGNETIC FIELD: The space in which a magnetic force exists.

MAGNETO: A generator that produces alternating current and has a permanent magnet as its field.

MAIN CONDENSER: A heat exchanger that converts exhaust steam to feedwater.

MAIN DRAIN SYSTEM: System used for pumping bilges; consists of pumps and associated piping.

MAIN INJECTION (SCOOP INJECTION): An opening in the skin of a ship designed to deliver cooling water to the main condenser by the forward motion of the ship.

MAJOR DIAMETER: The largest diameter of an internal or external thread.

MALLEABILITY: That property of a material which enables it to be stamped, hammered, or rolled into thin sheets.

MANIFOLD: (1) A fitting or header that receives exhaust gases from several cylinders. (2) A fitting that has several inlets or outlets to carry liquids or gases.

MAXIMUM OPERATING PRESSURE: The highest pressure that can exist in a system or subsystem under normal operating conditions.

MAXIMUM SYSTEM PRESSURE: The highest pressure that can exist in a system or sub-system during any condition.

MEAN EFFECTIVE PRESSURE (MEP): The calculated combustion in pounds per square inch (average) during the power stroke, minus the pounds per square inch (average) of the remaining three strokes.

MEAN INDICATED PRESSURE (MIP): The net mean gas pressure acting on the piston to produce work.

MECHANICAL ADVANTAGE (MA): The advantage (leverage) gained by the use of devices, such as wheels, to open large valves and chain falls; blocks and tackles to lift heavy weights; and wrenches to tighten nuts on bolts.

MECHANICAL CLEANING: A method of cleaning the firesides of boilers by scraping and wirebrushing.

MECHANICAL CYCLE: The number of piston strokes occurring during any one series of events (for example, 2-stroke or 4-stroke cycle).

MECHANICAL DRAWING: Scale drawings of mechanical objects. (See DRAWING.)

MECHANICAL EFFICIENCY: (1) The ratio of brake horsepower to indicted horsepower, or ratio of brake mean effective pressure to mean indicated pressure. (2) An engines rating, whichindicates how much of the potential horsepower is wasted through friction within the moving parts of the engine.

METERING: Accurate measuring of the fuel for the same fuel setting where exactly the same quantity of fuel will be delivered to each cylinder for each power stroke of the engine.

MHO: The unit of conductance; the reciprocal of an ohm.

MICRO: A prefix meaning one millionth.

MICROMHO: Electrical unit used with salinity indicators for measuring the conductivity of water.

MILLI: A prefix meaning one-thousandth.

MONITORING POINT: The physical loca-tion at which any indicating device displays the value of a parameter at some control station. See PARAMETER.

MOTOR: (1) A rotating machine that transforms electrical energy into mechanical energy. (2) An actuator which converts fluid power to rotary mechanical force and motion.

MOTOR CONTROLLER: A device (or group of devices) that governs, in some predetermined manner, the operation of the motor to which it is connected.

MOTOR GENERATOR SET: A machine consisting of a motor mechanically coupled to a generator and usually mounted on the same base.

NAVAL DISTILLATE DIESEL FUEL: The fuel normally used in diesel engines. The most commonly used for boilers and diesel engines is naval distillate (NATO symbol F-76), but other fuels such as JP-5 (NATO symbol F-44) and naval distillate lower pour point (NATO symbol F-75) are also used.

NEEDLE VALVE: Type of valve with a rod-shaped, needle-pointed valve body which works into a valve seat so shaped that the needle point fits into it and closes the passage. Suitable for precise control of flow.

NEGATIVE CHARGE: The electrical charge carried by a body which has an excess of electrons.

NEOPRENE: A synthetic rubber highly resistant to oil, light, heat, and oxidation.

NIGHT ORDER BOOK: A notebook con-taining standing and special instructions from the engineering officer to the engineering officers of the night watches.

NIPPLE: A piece of pipe that has an outside thread at both ends for use in making pipe connections. Various names are applied to different lengths, such as close, short, long, and so forth.

NITROGEN: An inert gas which will not support life or combustion.

NOMINAL OPERATING PRESSURE: The approximate pressure at which an essentially constant-pressure system operates. This pressure is used for the systems basic pressureidentification.

NONFERROUS METAL: Metal that is composed primarily of a metallic element, or elements other than iron.

NORMALIZE: To heat steel to a temperature slightly above its critical point and then allow it to cool slowly in air.

NOZZLE: A taper or constriction used to speed up or direct the flow of gas or liquid.

NOZZLE AREA: Smallest opening (area) of a nozzle that is at a right angle to the direction of flow.