Glossary
plumb bob
A plumb bob is a pointed weight hung on a cord. Gravity pulls the cord straight down, and the line it makes — a plumb line — is used to check that something is vertical.
A plumb bob is a pointed weight hung on a cord. Gravity pulls the cord straight down, so the line it makes is truly vertical — a plumb line — and the tool is used to check that a post, a wall or a frame stands upright rather than leaning.
Hold the top of the cord at the high point, let the bob swing and settle, and compare the gap between the cord and the work at the top with the gap at the bottom: equal gaps mean the work is plumb. The word means vertical, and it is the partner of level, which means horizontal.
Keep the bob clear of the work, since the weight is usually steel and will dent or chip what it touches, and let it stop swinging before you read it. A spirit level does the same job on a surface it can sit on, but a plumb bob reaches over an edge or down a wall where a level cannot rest.
Taught in
Related terms
- try square — A try square is an L-shaped tool with a thick stock and a thin steel blade set at exactly 90 degrees. It marks and checks square corners and straight edges.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)