I'm sorry. I don't understand. If I want to change the width of only one column then I put the mouse cursor on the right of that column and adjust only the width of that column. If that is not what you want to do, can you explain what you do want to do, please?
OK .. we have 2 situations in a pivot table .. if the pivot table has many expression .. you can do that gwessaner said .. but if the pivot table has 1 expressions and you moved 1 dimenssions over the expression .. for example .. month that has 12 possibles values .. you will have 12 possibles columns in the expression side and you can not have different sizes for tehm ..