Main Girder
A large, timber or steel beam used for supporting the joists of a floor or the framework of a building. 

Main Hoist 
The primary hoist of a large crane which would also have an additional hoist who can be used for smaller loads or whenever a large hoist is not necessary. It also helps to control the large loads of the primary hoist. 

Main Runner 
When installing a suspended ceiling, the main runner is the metal support, running the full length of a room to hold the cross tees which bridge the runners which are supported by wire attached to the old ceiling or over head beams.

Main Vent 
Ventilation system primary vent line. 

Main Water Shut-off Valve 
Primary valve, used to stop the flow of water, between the water meter and the home. 

Maintain 
1. To keep up or continue with something.
2. To keep in a certain condition or position. 

Maintain Contact Switch 
Electrical switch wired so that there are two switch positions from which two different modes can be run, such as high and low. A third position opens the switch so that current cannot flow, so that it functions as an on/off switch. 

Maintenance 
Periodic expenditure needed to preserve a property's original status rather than to improve that property. Activity required to compensate for wear and tear. 

Maintenance Bond 
Warranty bond given to guarantee that the necessary work will be done by the contractor doing repairs. This type of bond normally has a specific period of time. 

Maintenance Fee
Monthly assessment by homeowner's association on owners and used for maintenance and repair of common areas. 

Major Arch 
Also called Gothic, Tudor, parabolic, or semicircular arches, they are arches with a span of more than six feet with a rise-to-span ratio in excess of 0.15, having a load capacity of 1,000 pounds per foot. 

Major Diameter
The largest diameter of the threaded part of a threaded object. 

Majority 
The age at which one is no longer a minor and is fully able to conduct one's own affairs. Alternately, more than half. 

Make-up Air 
Air that is added to a room from which air is being removed, such as by an exhaust fan where the intake of fresh air would be make-up air. 

Make-up Water 
Water that replaces the water lost through evaporation or leakage, such as in a steam heating system. 

Maker 
Any person, company, or legal entity that signs a check or note to borrow money. 

Male 
The projecting, external part on anything. 

Male Fitting 
Pipe fitting that gets inserted into another fitting. 

Male Thread 
Thread on the external body of a tool. 

Mall 
A public area connecting individual stores in a shopping center. Modern malls are often enclosed, enabling all weather access. Also refers to an entire regional shopping center. 

Mall Stores 
Retail stores in a shopping center other than the anchor tenant, which is normally a larger store. 

Malleable 
The ability to be hammered, pounded, or bent into various shapes without breaking. Metals and other substances that are soft and pliable. 

Mallet 
Type of hammer, usually with a large wooden head, which is to pound on other tools or items, which would be marred by a metal head. 

Management 
1. Person or persons responsible for managing a property or overseeing a job. 
2. The act of managing, controlling or directing and carrying on a business. 

Management Agreement 
A contract between the owner of a property and the party who agrees to manage it. Fees are usually 4% to 10% of the rental income. 

Management Fee 
The cost of professional property management, with a fee typically set at a fixed percentage of total rental income generated by the managed property.

Management Survey 
Survey of the maintenance requirements for a commercial or industrial rental property for the purpose of preparing a management agreement. 

Mandatory 
Required. Being commanded to do or obtain something. 

Mandrel 
1. Metal spindle used in a lathe center to hold the work that is being turned.
2. Tool used to form. 
3. Threaded steel shank used in a rotary driver. 

Mandrel, Expanding 
Lathe mandrel that has lengthwise slots and a spring steel sleeve. To use this, the smaller end of the mandrel is pressed into place in the hole with an arbor press. To expand the sleeve tightly against the inside of the hole, a tapered pin is put inside the sleeve. 

Mandrel Test 
The roundness of a pipeline is tested by moving a slightly smaller steel shank, called a mandrel, through the inside of the pipeline. If the pipeline is out of round, the mandrel will be held and kept from moving forward. 

Manganese 
Grayish white metallic chemical element often used as a coloring agent. Atomic Number 25. Atomic Symbol Mn. Atomic Weight 54.938. 

Manhole 
Hole, with removable cover, through which a person can enter into a sewer, conduit, tunnel, etc. to repair or inspect. 

Manifold 
Piping from which other pipes lead to distribute to multiple locations.

Manila Paper 
Facing paper that covers the exposed side of gypsum wallboard to protect it prior to installation. 

Manometer 
Also called a draft gauge, this device is used to measure slight changes in a low-pressure system, such as an HVAC system, or for remotely measuring a level in a tank of liquid. One end of the U-shaped tube, which contains fluid and is marked with a graduated scale for measuring, is open and the opposite end is connected to the low-pressure source. The fluid in the tube is moved or displaced by slight pressure changes and the change can be read on the scale, which is calibrated to read directly in the desired units of measure. 

Manometer, Dry 
A different type of draft gauge, this device is used to measure slight changes in a low-pressure system, such as an HVAC system. When pressure changes occur they are measured by using a bellows and a pointer moving across a scale. The inside of the sealed flexible bellows, is connected to the source of low pressure so that the bellows will expand or contract with any change in pressure. The amount of change can be noted by reading the scale. 

Mansard Roof 
A four-sided roof that slopes upward from the edge of the roof to a square peak. This type of roof has two different slopes around all sides of the structure, the upper of which may be nearly horizontal and the lower nearly vertical. 

Mansion 
A large, imposing, stately home. 

Mantel 
The facing around a fireplace of stone, marble, wood, etc. or the shelf over any fireplace opening. 

Mantle 
Element used in a gas lap designed to emit a bright light. Made in the shape of a bag of coarse woven cloth, it is tied over the end of a gas pipe. A lighted flame causes it to burn briefly and turn into ash, which retains both the shape and strength of the original material but is brittle. The mantle diffuses the gas, allowing it to mix with air. The mantle glows brightly due to the gas that flows through and burns at its surface, making it useful as portable lanterns and exterior lighting. 

Manual 
1. A book of instructions for use as a guide or reference. 
2. Made, done, performed or operated by hand. 

Manual Brazing 
Brazing done by someone with use of a torch or arc welder. 

Manual Motor Starter
On/off switch equipped with a heating element that cuts off power to the motor when the normal current is exceeded. When the heater element temperature increases, it trips the switch to an open position and cuts off power to the motor. These starters are normally used for large motors. 

Manual Welding
Welding done by someone with use of a torch or arc welder. 

Manufacture 
To create something from raw materials. 

Manufactured Gas 
Gas, which has been created from coal. 

Manufactured Housing 
Partially factory-assembled units designed to be transported in parts and then assembled on the site. Prefabricated homes. 

Manufacturing Defects
Irregularities, which are happened while the item was being made. 

Manufacturing Milling Machine
Milling machine consisting of an adjustable (both height and width) table and a spindle head, which is height adjustable. This semiautomatic machine keeps the work being milled in place while the movement is done by the cutting tools. The machine is used for repetitive mill work.