Pilot balloon to Pitch

Pilot balloon to Pinion gear and shaft

(Mech.) A projecting part enter­ing a hole or opening, thus serv­ing as a guide for alignment of work.

Pilot balloon. (Aero.) A small bal­loon sent up to show the direction and speed of the wind.

Pilot drill. (Mach.) A small drill used to start a hole in order to insure a larger drill running true to cen­ter.

Pilot light. (Elec.) A small light set in a waIl case or receptacle at or near a control switch and wired to it to indicate whether the fixture or appliance connected to it is operating.

Pilot parachute. (Aero.) A smaIl, auxiliary parachute attached to the apex of the main parachute, designed to puIl the latter out of its pack when the rip cord is puIled.

Pimple. (Plast.) Undesirable smaIl, sharp or conical elevation on the surface of a plastic.

Pin. (Carp.) A smaIl peg or wooden nail. (Ceram.) One of various sized fire clay supports for ob­jects fired in a kiln.

Pincers. A jointed instrument with two handles and a pair of grasp­ing jaws for holding an object.

Pinch bar. (Shopwk.) A shop name for crowbar.

Pinch dog. (Wood Patmkg.) A small bar of steel, with two sharpened points projecting from it at right angles; used by wood workers for clamping pieces togehter when hand screws cannot be used.

Pine. (Wood) Includes a wide variety of woods, ranging from the soft, easily worked white pine to the hard, heavy, long-leaf yellow pine which is used in heavy construc­tion work. White pine is used prin­cipally for pattemmaking and for facework in dwelling construc­tion. Short-leaf yellow pine is used as a substitute for the long-leaf variety in places where great strength is not so necessary.

Ping. (Auto.) A short, sharp sound resulting from too rapid detona­tion of gas in the engine cylin­ders.

Pinhole. (Papermkg.) An imperfec­tion in paper which may be caused by froth or foreign particles. .

Pinholing. (Paint alld Lacquer) Minute holes in sprayed paint and lacquer ~lm due to bubbles which persist until the film has dried. Caused by draughts, sealed air pockets, humid spray booth, mois­ture or oil in air line, porous un­dercoatings, difference in tem­perature between surface being sprayed and the lacquer itself, or use of too-quick-drying thinner.

Pinion. (Gear.) The smaller gear of a pair, either bevel or spur, re­gardless of size. Pinion gear and shaft. (Auto.) The pinion gear and shaft, made as a unit from one piece of steel, car­ries the power from the propeIler shaft to the rear axle. The unit is supported by two tapered £oIler bearings; all are contained in a housing attached to the front of Piqua to Pitch of screw the chain type used for large pipes.

Piqua. (Wood) An African tree be­longing to the cedar family. It is a light brown, medium-hard wood, with grains somewhat like mahogany.

Pique. (Furn.) French inaly.

Piston. (Engin.) The plunger which moves within the cylinder of an engine or pump. The efficiency of compression depends very largely pn the proper fitting of the piston.

Piston head. (Auto.) The top, closed end of a piston.

Piston pin. (Auto.) A hollow steel shaft, hardened and ground, which connects the upper end of the connecting rod to the piston. It also is called "wrist pin".

Piston-pin bosses. (Auto.) Those parts of a piston which carry the ends of the piston pins.

Piston ring. (Mach.) A spring pack­ing ring for a piston.

Piston rod. (Mech.) The rod which moves the piston and is con­nected to the cross head or crankshaft.
Piston skirt. (Auto.) That part of a piston below the piston pin.

Piston stroke. (Auto.) The complete length of travel of a piston in its cylinder.

Piston valve. (Engine.) A piston operating in a cylindrical case .having ports which are opened and closed by motion of the piston.

Pit. (Plast.) Small, regular or irregular hole in the surface of a plastic, usually having approximately the same diameter and depth, and often dull or rough at the bottom.

Pitch.'(Chem. Plast.) A dark­coloured, fusible, viscous to solid bituminous or resinous substance, insoluble in water but more or less soluble in carbon disulphide, benzol, etc. (Mech.) A term used to denote the number of threads per inch, or in gearing, to indi­cate the size of teeth.

Pitchblende. (Mineral.) A dark min­erai with pitch like IUliter. An ore containing uranium and radium.

Pitch board. (Bldg.) A template of thin wood or metal, in the shape of a right-angled triangle, for marking out and testing the cuts of a stair string. The shorter side is the height of the riser cut; the next longer side is the width of the tread cut.

Pitch circle. The circumference of the pitch line; the circle of con­tact in meshed gears.

Pitch diameter. (Gear.) The diam­eter of the pitch circle of a gear wheel.
Pitch indicator. (Aero.) An instrument for indicating the existence of a . pitching velocity of an aircraft.

Pitch of a roof. (Arch.) The angle which the slope of a roof makes with the horizontal.

Pitch of a screw. (Mach.) The dis­tance from a point on a screw thread to a corresponding point on the next turn. In a single thread the pitch is the amount of advance