Diagonal
1. A line, in a rectangular figure, running at angle from the middle of an angle to the middle of an opposite angle.
2. Moving or extending at a 45-degree angle.
3. Slanted markings or lines across a surface.

Diagonal Board Fence
Style of fencing with flat boards installed diagonally between the top and bottom railings.

Diagonal Bracing
Boards which are installed diagonally across the wall studs to keep the walls from racking or going out of square and to add strength to the structure. Each stud is cut where the bracing board will fit so that it is flush with the studs on the surface.

Diagonal Cutters
Wire cutters that are shaped like pliers with the axis of the cutting edge parallel to the axis of the handles.

Dial Indicator
This precision gauge, which is also called an indicating gauge, consists of a plunger that has gear teeth cut along parts of its length to engage a gear on the indicator needle to provide a visual indication of even very slight variations in the grade of a surface. The gauge, which has a needle that passes around the precise dial, which shows gradations as small as one ten-thousandth of an inch, is tightly clamped to a rigid surface, then the plunger is adjusted to connect with the work which is to be measured. This work is then moved past the plunger, which provides readings of the variations in the surface. When precision measurements, such as centering a piece of work in an independent chuck on a lathe, this gauge is valuable.

Diameter
Distance of a straight line passing through the center of a circle or sphere from one side to the other.

Diamond
Mineral consisting of almost pure carbon in crystalline, which was formed under pressure and is the hardest natural substance known.

Diamond Drops
Droplets of sap that appear on the surface of painted wood.

Diamond Point Chisel
Metal cutting tool for cutting V-shaped grooves or to make sharp corners in holes by use of a V-shaped cutting edge.

Diaphragm
1. Any partition or membrane separating one thing from another.
2. Thin, flexible disk that vibrates in response to sound waves, producing electrical signals or vibrates in response to electrical signals, producing sound waves.
3. Structural sheathing, which may be applied over framing; between the webs on a bridge crane girder, acting as a load-bearing unit.

Diaphragm Action
On a structure, a stressed skin, which resists movement, by providing stiffness that could distort the structural square, shape.

Diaphragm Tank
Partitioned expansion bank with the gas and water separated so that no gas can be absorbed into the water system.

Diaphragm Valve
Valve which is used for fluid control or for shutting off pipeline fluids or gasses from coming in contact with the operating parts of the value, due to the threaded stem which forces a compressor plug against the diaphragm.

Diatomaceous Earth or Silica
Chalk-like gray or white silicon, composed of fossilized remains of marine life, which is used for thermal insulation for steam piping, paint extenders, scouring powders, filters, etc. Also called Tripoli or Infusorial Earth.

Diazo
Photocopying method, which uses a coating of a diazo compound on the paper that makes it sensitive to ultraviolet light, so that when exposed to light, it decomposes.

Dictum
Judge's remark in a court ruling not in and of itself embodying the law, it merely illustrates or amplifies the ruling. Alternately, the ruling made by an Arbitrator.

Die
1. Any of various tools for molding, stamping, cutting or shaping.
2. The stationary part of a machine for shaping or punching holes in sheet metal.
3. The mold, which holds the molten metal.

Die Cast
The casting of molten metal in a die.

Dielectric
Non-conducting material that is an electrical insulator.

Diesel Engine
Type of internal combustion engine that burns fuel oil with the ignition brought about by heat resulting from air compression rather than by an electric spark as it is in a gasoline engine.

Diesel Hammer
Type of machine for driving pilings, which uses diesel combustion to raise the hammer.

Differential
Having different effects or results. The difference between two consecutive values.

Differential Gear
A certain arrangement of gears connecting two axles in the same line and dividing the driving force between them, but allowing one axle to turn faster than the other. Often used in the rear axles of automobiles to allow a difference in axle speed for turning curves.

Differential-Acting Hammer
Type of machine for driving pilings, which uses air or steam to drive the hammer.

Differential Leveling
Using a level and rod to determine a difference in elevation between two points.

Differential Pressure
Pressure difference in two parts of a system or two areas.

Diffraction
Energy redistribution due to an obstruction or change in the surface over which it is passing. Diffuse 1. To pour in different directions. 2. Spread out or dispersed, not concentrated.

Diffuser
1. A device that distributes light evenly.
2. HVAC air outlet, which directs air widely in a fan-shaped pattern.

Diffusion
1. Scattering of light rays as by reflection; the softening of light as by use of frosted glass.
2. Intermingling of the molecules of liquids or gases.
3. Dispersing or spreading out.

Diffusion Welding
Welding process joining parts, without deforming them, by use of heat and pressure because they are not melted or moved.

Dig and Set
Also called cut and cover, this method of laying pipe and trenching eliminates the need to remove a large amount of dirt by using the soil from one section to cover the pipe in an adjoining section. Therefore, only the original soil must be removed, since the rest is buried as the work progresses down the line.

Digital Images
Pictures incorporated into home listings to give a view of the property.

Dike
1. An embankment or dam made to prevent flooding by a body of water.
2. A protective barrier.

Dilapidate
To cause to become partially ruined and in need of repairs.

Dilate
1. To make wider or larger.
2. To cause to expand or swell. Dilute To thin down or weaken by mixing with other liquid.

Dilution
Adding other weld metal or having the base metal melting and mixing with the weld filler metal to change the composition of that weld filler metal.

Dilution Ventilation
Ventilation needed to reduce the level of contaminants in an area being ventilated.

Dim
1. Somewhat dark; not bright.
2. Without luster; dull.
3. Decrease the amount of light.

Dimension
Measurements in length and width and usually depth.

Dimension Line
Identification of distance between two points by use of a line on a drawing. Frequently used on blueprints to display room lengths and widths.

Dimension Plans
Plans, less detailed than full blueprints, showing the layout of a house.

Dimension Ratio
The identifying of various hub and spigot types of plastic pipes is usually done by taking the dimension ratios of the average outside diameter of plastic pipe to its minimum wall thickness, rounded to the nearest 0.5. These standard dimension ratios (SDR) are internationally recognized.

Dimensional Lumber
Lumber precut to standard dimensions, which are typically, 2 to 5 inches thick or 5 to 12 inches wide.

Dimensional Shingles
Shingles that are manufactured in uniform, rather than varied, sizes.

Dimmer Switch
Electrical switch used to reduce the amount of light coming from a fixture.

Dimple
1. Any hollow or depression in a surface.
2. Depression left by a nail being set by hammer in the surface of sheetrock.

Diode
Electron tube of the high-vacuum type which a cold anode and a heated cathode, which is used to allow current to pass in only one direction.

Dip Brazing
Process of brazing which uses heat from molten chemicals or metal bath.

Dip Needle
Freely moving, vertically suspended magnetic needle which is used to indicate the direction of the earth's magnetism; horizontal at the magnetic equator, vertical at the magnetic poles.

Dip Tube
An extension of the water supply line into a storage tank to deliver water close to the heating source on the bottom of a water heater.

Dipole
1. System which has two equal but opposite electric charges or magnetic poles separated by a small distance.
2. Molecule with the centers of positive and negative charge separated.
3. Electrical set of poles with a switch, which can turn on two electrical lines simultaneously.

Dipping
Immersing in liquid.

Dip Soldering
Process of soldering which uses heat from a molten metal bath of solder.