A plumb bob

A plumb bob, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line.
The plumb line is used to set the rails in a vertical position for vertical adjustment when leveling an uneven position
The plumb line is widely used in construction and earthmoving.
Print models. Pour sand, shot or the like into the bottom of the bottom to make it heavier. Glue the top.
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