set linewidth <value>
The set linewidth command sets the default line width of the lines used to plot datasets onto graphs using plot styles such as lines, errorbars, etc. The value supplied should be a multiplicative factor relative to the default line width; a value of 1.0 would result in lines being drawn with their default thickness. For example, in the following statement, lines of three times the default thickness are drawn:
set linewidth 3 plot sin(x) with lines
The set linewidth command only affects plot statements where no line width is manually specified.