Fluctuate
To be continually changing or varying in an irregular way.

Flue
Passageway by which byproducts from combustion leave a chimney.

Flue Lining
Heat resistant lining, usually of fire clay or terra cotta pipe, used for the inner lining of chimneys.

Flue Pipe
Airtight conduit constructed within a chimney using fireproof materials to carry away combustion gases and smoke occurring in a furnace or firebox.

Fluid
Substance that flows and changes shape.

Fluidics
Technological application of fluids to perform functions, such as controlling mechanisms using hydraulic pressure and flow. Fluid Mechanics Science governing the behavior of fluids.

Fluid Ounce
Fluid volume measure which equals 1/32 quart.

Flume
1. Narrow ravine with a stream of water running through it.
2. An artificial channel serving as a chute for carrying water to furnish power or to transport items.

Fluorescence
Ability of a material to emit radiation, visible or invisible, upon receipt of certain stimulation such as ultra-violet rays or x-rays.

Fluorescent Lamp or Light
A glass tube coated on the inside with a fluorescent substance that gives off light when mercury vapor in the tube is acted upon by a stream of electrons from the cathode.

Fluorocarbon
A class of non-reactive organic compounds that contain carbon and fluorine combined to be used in lubricants, cleaners, fire extinguishers, aerosols, etc.

Flush
1. To flow and spread suddenly or rapidly.
2. To become cleaned, washed, or emptied out by a flow of water.
3. To be even or on the same plane with surface.

Flush Ball Valve
The outlet valve in the tank of a toilet, which includes a guided stopper in the tank, itself and a device, which connects the stopper to the handle for flushing. When the handle is pressed, the handle lifts the stopper out of the water in the tank, which allows the water in the tank to drain out through to the bowl of the toilet. Once the handle is released and the water level is lowered, the stopper is pulled back into the water tank. When the stopper is returned to the outlets, it seals and does not allow any more water to flow out of the tank until the handle is pressed again.

Flush Device Box
Electrical box which has tapped holes to fasten switches or outlets flush with a surface.

Flush Door
Door with a plywood facing over the internal core of wood or wood products. A hollow core door is one with plywood facing over framework without a solid core.

Flush Ell
Also referred to as a water closet ell, this elbow fitting goes between a wall-hung tank and the bowl.

Flush Joint
Also called a rough-cut joint, this mortar joint is troweled level and flush with the brick face.

Flush Plug
Plug which screws into a floor mounted electrical box.

Flush Weld
Weld that is even with the surrounding base metal.

Flush-mount Lavatory
Sink which sits flush and even with the countertop and is supported by a metal ring.

Flushometer
Toilet valve that automatically shuts off after it meters a certain amount of water flow.

Fluting
Decorative molding made of a series of rounded outwardly curved channels, adjoining each other along the length of the molding.

Flux
1. Compound, which combines during refining with impurities in molten metals.
2. Chemical that isolates heated metal from the oxygen in the air, aiding in the removal of oxidation during welding, soldering or brazing and allowing better metal flow in the joint.

Flux-cored Arc Welding
Arc welding that is done by feeding filler metal and flux through the enter of the electrode from which the arc travels to the base metal.

Flux-cored Electrode
Hollow consumable welding electrode that has a flux core.

Fly Cutter
Cutting tool, attached to a shaft or arbor, which is used to cut circular sections out of material. A drill motor turns the arbor making the bit revolve around the arbor. The adjustable arm can change the diameter of the hole that can be cut, by increasing or decreasing the distance of the bit from the arbor.

Flying Levels
An approximation of elevations made when surveying.

Fly Rafter
Also referred to as a barge rafter, it is the rafter at the gable end that's attached to the roof sheathing above and the lookout blocks, which are behind the rafter.

Flywheel
Wheel that is attached to a rotating shaft to reduce fluctuations or pulsations in its rotation by the addition of weight.