Each selection is a column that auto adjusts to the labels used. No label, no need to adjust. You might be able to fool it with an invisible label on the empty ones or use CSS to force a standard width. If I may, I know this isn't what you asked but why are you using 10 choices to spread out a 5 point unipolar likert? Is there really a need for two distinct degrees between Not Knowledgeable and Slightly Knowledgeable? Maybe the answer is to just reconsider the number of choices?