It can be used to make sure that constructions are plumb, but it can also be used in surveying to establish the nadir with respect to gravity at a specific point. Precisely machined and balanced bobs have pointed tips, and can be made of brass, steel, or other materials, including plastic. A plumb bob is a pointed weight attached to the end of the string and is used to find a vertical reference line called plumb. PLUMB BOB meaning: 1 : a usually small, heavy object that is used to make a string or rope hang straight the heavy object that is part of a plumb line. A plumb bob is a weight with a pointed tip on the bottom that’s hung from a string, and it’s used to establish a vertical reference (called a plumb line). (Masons prefer nylon because it stands up better over time to the dampness that comes with the trade.) At one end of the string the weight is affixed. The plumb consists of a specially designed weight and coarse string made of twisted cotton or nylon threads.
In a sense, the plumb bob is the vertical equivalent of the line level.
You don’t have to be a physics whiz to understand that a string suspended with a weight at the bottom will be both vertical and perpendicular to any level plane through which it passes. The plumb bob or plumb line employs the law of gravity to establish what is “plumb” (that is, what is exactly vertical, or true). As is so often the case, it isn’t how fancy the tool is, but how well you use it. For most home toolboxes, I recommend having a single bob that weighs a few ounces. (It’s also thought that, in tandem, they used flooded ditches to determine levels.) Plumb bobs may weigh as little as an ounce or as much as several pounds, depending upon the application.
Evidence suggests that Egyptian architects used plumb bob-like tools to establish verticals in constructing the pyramids.
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