Purlin

purlin A horizontal beam, strut, timber, or support in the framing of a roof system and usually supporting the roof decking.

purlins

pustule A raised bump on a plant much like a blister.

putty A heavy paste composed of pigment mixed with linseed oil and used to fill holes and cracks in wood prior to painting.

putty knife A tool with a long handle and a flat-nosed blade used for spreading putty.

PVB Abbreviation for pressure vacuum breaker.

PVC Abbreviation for polyvinyl chloride, a common plastic material from which pipes are made, and is often the choice for use in constructing sprinkler irrigation systems. Pipes and fittings of this material are classified for various pressures with the pressure rating stamped on the side, or with the thickness of the pipe stamped by reference to schedule. It is not resistant to impact, especially in smaller sizes or with thin walls. It is sold in schedule or class sizes. Connections may be made by solvent weld, threads, or by compression fittings with rubber gaskets, depending on the type of connection it is prepared with.

pylon sign A sign that towers above the surrounding landscape or buildings. (Compare with monument sign.)

pylon sign

pyramidal A botanical term describing a shape that resembles a pyramid: broad at the base and tapering to a point. It may describe a plant part or a plant outline of its head, such as many evergreen trees. (Compare with round, columnar, fastigiate, oval, broadly spreading, upright spreading, weeping.)

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