Linewidth changes the thickness of lines in the default wireframe representation. The default width of 1.0 can be changed to any positive number, although reasonable values will generally be under 5.0. Rendering thicker lines requires less computational power than changing to a stick representation, so may be preferred for large structures.
If the atom-spec is blank, all open molecule models will be affected; otherwise, the entire model(s) containing atom-spec will be affected. If an affected model is in an alternate representation (stick, sphere, etc.), the change in linewidth will not be evident until part or all of the model is changed to wireframe. Linewidth can also be changed in the molecule model attributes panel.
See also: represent, wire width in the Actions menu