Drop 
1. Horizontal section on a vertical scaffold. 
2. HVAC system term for the distance air has fallen vertically below an outlet at the point of the air's terminal velocity. Alternately, where the air velocity coming from an outlet decreases to 50 feet per minute. 

Drop Chain 
Small link, weighted chain used to feed an electrical wire into a vertical passage. 

Drop Cloth 
Large piece of cloth, plastic, etc. used for protection against dripping paint or other messy jobs. 

Drop Forge 
Machine which forges metal by heating it to a malleable temperature and using weight to hammer the metal to provide the needed shape and size. 

Drop Hammer 
Casting made of heavy steel, which is raised and then dropped, from a certain height to drive pilings into the ground. 

Drop Leaf 
Table extension, which is hinged to a side, so that it can be folded under when not needed. 

Drop Light 
Electric light on a long cord hanging over a work area, providing direct lighting. 

Drop Outlet 
Gutter system fitting, which feeds into a downspout to drain water that has collected in a gutter. 

Drop Siding 
Siding boards with a tapered cross-section, of which, the top edge is narrower. Installed horizontally, the top edge fits into a groove in the bottom edge of the board above it. 

Dropped Ceiling 
Flat ceiling, which is built lower than the original ceiling. 

Dropping a Hip Rafter 
To prevent the upper edges of a hip rafter from projecting over the plane of the adjoining roof, a deep seat cut is made so that the hip rafter sits lower than the surrounding roof framing. 

Drum 
1. Any of various drum-like cylindrical objects or containers. 
2. Rotating, power-driven cylinder used as a hoist by wrapping a hoisting rope, which is attached by a pulley or pulleys, to the load being hoisted. 

Drum Sander 
Rubber drum, mounted on an arbor, which is held in the chuck of a motor that turns, thereby rubbing its cover of abrasive material, against the work that is held against it for sanding. 

Drum Trap 
Plumbing fixture, which is cylindrical in shape, which retains water as a seal, with an outlet at its top and an inlet at its base. Used in plumbing fixtures that are too low to the floor for installation of a P-trap. 

Dry Battery 
Sealed electrical storage battery that contains no free liquid. 

Dry Bulb 
Thermometer Instrument which measure the amount of heat in the air by the expansion f a liquid in a graduated glass tube with a reservoir bulb at one end. Alternately, by use of a bimetallic strip which moves the indicator on a scale when heat causes the two metals to expand at different rates. Normally used for outdoor temperatures. 

Dry Gas 
Also called sweet gas, this natural gas has all impurities removed. 

Dry Masonry 
Masonry that is set without using mortar. 

Dry Mix 
Packages of dry mix containing all the ingredients (cement, sand & gravel) needed for making concrete or mortar when water is added. 

Dry Mortgage 
Creates a lien against the mortgagor's property, but does not permit a lien against his/her personal assets. 

Dry Rot 
Brown, crumbling look of wood, which is decaying due to fungi. Rather than dry, this type of deterioration occurs when wood is subjected to a constant source of moisture, such as studs, when there is a leak 

Dry Taping 
Use of joint tape, using adhesives other than joint compound, for wallboard. 

Dry-pipe Sprinkler System 
Protection system for fire using air pressure to keep the pipes free of water until the system is activated. 

Dry-press Brick 
Brick made, under high pressure, of clay with a 5 to 7 per cent moisture content. 

Dry-set Ceramic Tile Grout 
Portland cement, sand with additives having water retention abilities, mixed together to be used grouting walls and floors with only normal use. 

Dry-set Ceramic Tile Mortar 
Portland cement and sand with additives having water retention abilities, mixed together to be used for bonding ceramic tile to a base. 

Dry-stone Wall 
Stone laid for a wall without the use of mortar. 

Dryer Receptacle 
Electrical outlets for a clothes dryer must be 240 volt, 30 ampere. 

Drying Oil 
Oils, derived from certain plants and which dry to a solid in the open air, provide good protective coating for wood. 

Drywall 
Gypsum or plaster wrapped construction material, produced in large sheets to be nailed to wall studs. Also called Sheetrock, wallboard or plasterboard, it comes in a variety of sizes: 4' wide in 6', 7', 8', 10', 12' and 16' lengths and 3/8', ½" and 5/8" thicknesses. The 5/8" thickness comes in only the 4' X 8' size because of its weight and is normally used to fireproof walls. 

Drywall Blisters 
Gypsum wallboard defect, which allows the facing paper to become unattached from the gypsum core. 

Drywall Construction 
The construction of stone or block walls without using concrete or mortar; traditionally used for fieldstone wall construction. 

Drywall Hammer 
Handheld tool, which has a flat striking surface on one end of the head, which is, used with gypsum drywall nails. The other end of the head has a hatchet-like blade, which is dull and used for prying instead of cutting. 

Drywall Knife 
Also referred to as a taping knife or a putty knife, it's flat-bladed and comes in various widths. 

Drywall Saw 
Coarse toothed saw with a blunt end that is used to cut drywall. Drywall T-square Larger sized T-square, which is used when laying out, cuts on drywall.