A straight edge perhaps?
The instrument that is used to construct straight lines is called a rule. Often people make the mistake of calling it a ruler, but its a rule.
A straight edge or a ruler are used to construct straight lines.
A straight-edge
A straight edge or a rule are used to construct straight lines. Laser line setter, In some cases a plumb line
That's commonly known as a "straight edge".
An instrument to construct straight lines is called a rule. It's often referred to as a ruler, but a ruler is someone who rules a country. A rule is a piece of wood, metal or plastic (usually showing measurements) that you can use to draw/construct straight lines.A straight edgeThe most common one is a ruler
a pencil
COMPASS
Compass
ruler
In construction, all you need is a compass and a ruler.
It is "a pair of compasses" - usually called a compass.