This example adds a combo box control to a command bar. Two items are added to the control, and the number of line items and the width of the combo box are set.
Set myBar = CommandBars("Custom")
Set myControl = myBar.Controls.Add(Type:=msoControlComboBox, Id:=1)
With myControl
.AddItem "First Item", 1
.AddItem "Second Item", 2
.DropDownLines = 3
.DropDownWidth = 75
.ListHeaderCount = 0
End With