How to Add thickness in a particular Curve in Rhino 4 

following picture can guide you to add thickness to any curves 
by adding few simple steps while modelling.

1. Step 1

   Draw curves and type ( in command Bar ) or click on "options" icon

   

2. Step 2

   In rhino options click " Appearance "

   

3. Step 3

   As soon as you click " Appearance " a drop down pop up will open 
   as " Advance setting "

   

4. Step 4

   Click in the " Advance setting " button , you will see " Advance Display setting "and then click on any viewport names , 
   in this tutorial I have used wireframe .

   

5. Step 5

   At the bottom of the pop out menu ( Rhino options ) you will find a copy button, 
   this button will make a duplicate copy of the selected viewport. Thus as soon as you hit the button ..

   

6. Step 6

   immediately a " Display mode options " window will open, that says " copy of wireframe"

   

7. Step 7

   Now under " copy of wireframe" we can see " -objects " which is further 
   having settings for various objects namely ; points, curves, surfaces and meshes . As we need to add width thickness on the curves ( polylines, ect) 
   click on curves button/ tab , upon that you will see " Curve width pixels "

   

8. Step 8

   edit that column as per your requirement ( I have edited it to 5 pixels ). 
   than press/ click " ok " 
   ( the settings gets saved)

   

9. Step 9

   Now select the curve you want to add thickness to ( I have selected a circle )

   

10. Step 10

    now in command bar type ( keep curve selected ) 
    " setobjectdisplaymode " 
    and press enter key

    

11. Step 11

    Choose attribute for selected object 
    ( the selected curves will show the changes only in the active view , i.e in the view in which it is displayed ) 
    click on " mode " 
    or type " M " in key board and press the space key

    

12. Step 12

    ON clicking that you will see all the viewports including " copy of wireframe " ( which we recently created. Choose " copy of wireframe "

    

13. Step 13

    As soon as you click on the " copy of wireframe " 
    the command gets over and you find that the curve which is selected have a 
    different width thickness than other curves. This change in display can be 
    reversed by same method 
    ( just click on " user view " in choosing attributes )

    

14. Step 14

    Enlarge the veiwport and inspect, this will not change its apperence in other viewports , you will have repeat same steps in different veiwports in order to see the effect

    

15. Step 15

    Now if you want to see the similar kind of effect in you prints also than he 
    under object properties

    

16. Step 16

    There is print width option in the bottom of the op out menu. 
    by default its layers , so click on that and..

    

17. Step 17

    edit the value

    

18. Step 18

    Than go to print command

    

19. Step 19

    As soon as you execute the command you can see the 
    curve in different width in the print preview.

    

20. Step 20

    I hope this is helpful :)

    

21. Step 21