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“M” Tubing – An industry standard for copper tubing defined by the tube wall thickness, identified by a “red” stripe.
MC Tank – Acetylene tank holding 10 cu. ft. of gas, used for plumbing, once used to fuel motorcycles.
MCL – Maximum Contaminant Level The maximum level of a contaminant allowed in water by federal law. Based on health effects and currently available treatment methods.
MHT – Male Hose Threads (threads on outside of connection)
MIP – Male Iron Pipe Connection. Standard external threads on pipe and fittings.
MNPT – This refers to the male pipe thread, in which the threads are on the outer side on the connection fitting.
MPX – Male Pipe Swivel Connection
Macerator – A device installed in a drain line between a toilet and the soil stack to reduce solids to liquid form.
Main – The primary artery of supply of the water supply or drain system in which all the branches connect. In the case of drains, known as the Main Vent.
Male Fitting – Fitting that is inserted into another fitting.
Male Threads – Threads on the outside of pipes and fittings.
Malleable Fittings – Fittings made of cast iron. Metal which is soft and pliable.
Manhole – Access opening to a hole, usually with a cover, through which a person may enter a sewer, boiler, drain, etc. (usually round to prevent the cover from falling into the opening).
Manifold – A fitting that connects a number of branches to the main; serves as a distribution point.
Manifold Pressure – The gas pressure in an appliance manifold upstream of the burner orifices.
Manifolded Installation – Paralleling of water heaters for large hot water demand applications.
Mapp Gas – A colorless, flammable gas made by combining liquefied petroleum gas with Methylacetylene-Propadiene. It is a stable, non-toxic fuel used in brazing and soldering.
Mechanic’s Lien – A lien obtained by an unpaid subcontractor or supplier through the courts. When enforced, real property – such as your home – can be sold to pay the subcontractor or supplier.
Mechanical Controls – Dials, slides, switches, knobs, buttons, and so forth used to operate ranges, ovens and cook-tops.
Mechanicals – The wiring, plumbing and heating and cooling systems in a building; also the components with moving parts such as furnaces, plumbing fixtures, etc.
Metal Fatigue – A breakage of the metal caused by the bending and flexing or the expansion and contraction of a metal part beyond its endurance limit.
Meter Tailpiece – An adapter connecting a water meter to the water supply line.
Meter Tile – The cylindrically shaped casing that forms the pit to hold a water meter. It’s usually made of plastic.
Micron – A unit of measure, one thousandth of a meter. Used to describe the pore size of filters.
Mini-Widespread – A special style of bathroom lavatory faucet having separate spout and handles, but small enough to fit 4 inch center-to-center faucet holes.
Minimum Run Time – The minimum length of time that the pump should run while refilling the pressure tank.
Mission Coupling – A neoprene flex coupling, connecting PVC to PVC or clay to PVC.
Mixer – The portion of a burner where air and gas are mixed before delivery to the burner ports.
Mixing Valve – Mixes hot and cold water to achieve a specified delivery temperature.
Moenstone – A blend of ceramic-like quartz (70%) and acrylic polymer (30%) that is impervious to chips or water spots.
Monitor Cover – The cast iron lid that fits over a flange casting which is mounted on meter tile in a water meter pit. It consists of an outer lid, an inner lid, and the flange casting in one or two pieces.
Monoblock Faucet – A single-handle faucet, usually a lever.
Most Probable Number (MPN) – The term used to indicate the number of organisms which, according to statistical theory, would be most likely to produce the results observed in certain bacteriological tests; usually expressed as a number in 100 ml of water.
Multiport Valve – Rotary type backwash valve. Can replace up to 6 regular gate valves. Serves various functions.
Multi-Stage Pump – A pump that has more than one impeller.
Municipal Water – Water supplied by a city for public use; tap water. Usually held in a reservoir.
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Source: “Plumbing Terms” Standard Plumbing Supply. 11 Sept. 2008