The term “fire plug” dates from the early 1800s, when water mains were made of wood. When responding to an alarm, firefighters had to chop into the main waterline to connect their hoses. When they finished fighting the fire, they would seal the main with a “fire plug.”

An Allen wrench has a hexagonal cross-section.

A regular polygon has sides the same length and interior angles the same size.

Each of the diagonals of a regular pentagon is parallel to one of the sides.

The names pentagon and hexagon describe their respective numbers of angles (or sides). Early Greek mathematicians studied these shapes and gave them their names:

 Number Greek 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

Also, -gon comes from a word meaning angle.

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