You can control the thickness of an object’s lines in both the drawing display and plotting.
Lineweights can be turned on and off in a drawing, and are displayed differently in model space than in a paper space layout.
The current lineweight is the lineweight used for any objects you draw until you make another lineweight current.
You can change the lineweight of an object by reassigning it to another layer, by changing the lineweight of the layer the object is on, or by specifying a lineweight for the object explicitly.