Click the plot to select it.

From the context panel, select Line.

Select Line Width. The Set Line Width dialog opens.

Increase or decrease the line width using the arrow buttons, or enter a line width greater than 0.

Click OK.

Click the plot to select it.

From the context panel, select Line.

Select Line Width. The Line Width dialog opens.

Enter a line width between 1 (narrow) and 50 (wide), or change the line width value using the Slider.

Click OK.

When using the plot and plot3d commands, line width can be set using the thickness=n option. The value of n can be any positive integer. For details, see plot[options] and plot3d[option].