A plumb bob is a weight, (usually made from Brass), with a pointed tip at the bottom, that is suspended from a string. This creates a straight vertical line that can be used as a reference line. Plumb bobs only read accurately if they hang freely and the weight is completely still.
Often used in construction surveyors use plumb bobs for lining up points or transferring them. Mainly used in excavation and foundation construction they are also very useful when building walls, doors or hanging up wallpaper and pictures or anything that requires a straight vertical line.
Plumb bobs come in different shapes, sizes and materials