"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).

MIPC

Male Iron Pipe Connection. Standard external threads on pipe and fittings.

MNPT

Refers to the male pipe thread, in which the threads are on the outer side on the connection fitting.

MPN

See Most Probable Number

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.

Magnesium

One of the elements in the earth's crust, the compounds of which when dissolved in water make the water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.

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.

Manganese

An element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentration; causes black stains and other problems similar to iron. It can be removed by a water softener or it can be precipitated by chlorine at a pH of 9.5 or above.

Manganese Greensand

Greensand that has been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power, and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and in their removal from water.

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 liquified 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.

Millivolt

One thousandth of a volt.

Mini-Widespread

A special style of bathroom lav 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.

Moenstone³

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.

Monobloc Faucet

A single-handle faucet, usually a lever.

Most Probable Number

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

Multi-Port 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.