I wnat to specify the width of the toolbar

The width of the vertical toolbars depends of the content of the toolbar. So if you have the option "Show Text" is turned on for toolbar then the toolbar width can become too large because the text of some can be too long. So you can to reduce the text for buttons or use the options "Max width of buttons with text" in the TLB Settings->Metrics. Other option you maybe need: TLB Settings->Toolbar->Same width for all buttons with text