How to adjust the thickness of SOME lines in a Word table?

Are you trying to do this with table styles, or just for an individual table?

• For an individual table you just need to select the row and click Borders and Shading to update just that row. Make sure you select "Custom" on the left hand side under Setting, to make sure you can play with individual lines. Use the Style and Width to set what sort of line you want and then adjust on right hand side by clicking the lines you want to change.

  It is important to first select Thickness, then the line you want to change. So, under Borders and Shading select Custom, then Color (if needed), select Thickness, then select Line you want to change.

  

• For a table style, you need to go to "Apply Formatting to" and select the type of row you want to change (header, odds, evens, total, etc.) You can't do this for a random row though.

I finally figured it out: Under Table Tools/Design menu, go to Draw Borders and adjust the line values to your preference. Then click on Draw Table and a pencil icon will appear. Click on any line and voila! The line is now set to your liking.

It could be done quickly with the border painter tool

• Click inside the table to make the table tools group appear, then on the ribbon select Design tab
• In the Borders group select whatever line style you want
• Click Border Painter. The mouse will change to a brush (a pencil in prior versions of MS Office). Clicking the brush on any line in the table will change that line to the style you choose