Hi RAM,
I believe that with the Control Toolbox (ActiveX) controls the dropdown arrows and other similiar features are designed to maintain a consistent look with other windows controls, which is why we are not give a property we can change to set the dropdown arrow width. As a result, I'm pretty sure that you have to change ALL dropdown arrow widths--which you can do from the Windows Display Properties dialog (right-click on the windows desktop, select Properties, select the Appearance tab, select "Scrollbar" in the Item dropdown, then set the Size property. Note that "arrows" include those at the ends of scrollbars, etc.
Damon