You can change the current lineweight of an object by reassigning the object to another layer, by changing the lineweight of the layer the object is on, or by specifying a lineweight for the object explicitly.
Set the Current Lineweight
All objects are created in a drawing using the current lineweight. You can change the lineweight in the Lineweight control on the Properties toolbar, or in the Lineweight Settings dialog box.
If the current lineweight is set to BYLAYER, objects are created in a drawing using the lineweight assigned to the current layer.
If the current lineweight is set to BYBLOCK, objects are created using the default lineweight, until the objects are grouped into a block. When the block is inserted into a drawing, it acquires the current lineweight setting.
To specify a lineweight for the current layer that is different from the current lineweight, open the Layer Properties Manager and give a specific value.
By default, the lineweight of an object is set to BYLAER, and the lineweight of a layer is set to DEFAULT. Lineweight that is assigned to objects is displayed as a solid fill drawn in the object's assigned color.
To set the current lineweight
Choose Format > Lineweight.
In the Lineweight list, choose the lineweight that you want to make current.
Command line LINEWEIGHT
TIP On the status bar, click the LWT button to toggle the display of lineweights on and off.
NOTE To see lineweights in your drawing, you may need to turn on lineweights.
Change the Lineweight of an Object
There are three choices for changing the lineweight of an object:
If the lineweight of an object is set to BYLAYER, and you reassign the object to a different layer, the object acquires its lineweight from the new layer.
If the lineweight of an object is set to BYLAYER, you can change the lineweight of the layer the object is on, and all objects assigned to BYLAYER on that layer are updated automatically.
Specify a lineweight for an object to override the layer's lineweight. If you want to specify a lineweight to override the layer-determined lineweight of an object, change an existing object's lineweight from BYLAYER to a specific lineweight.
In order to create subsequent objects using a new lineweight, you have to change the lineweight setting on the Properties toolbar from BYLAER to the specific one.
LWEIGHT: Sets the current lineweight, lineweight display options, and lineweight units
PLINE: Creates two-dimensional polylines
LAYER: Manages layers and layer properties
PEDIT: Edits polylines and three-dimensional polygon meshes
PLOT: Plots a drawing to a plotter, printer, or file
System Variables Reference
LWDISPLAY: Controls whether the lineweight is displayed on the Model or Layout tab
PLINEWID: Stores the default polyline width