Make combobox list options dependant on selection in another combobox within a userform

Hi,

I have an Excel workbook with a front sheet containing a Userform named "Package_Size".
"Package_Size" has two Comboboxes: "Commodity_Selection" and "Size_Selection"
I need the dropdown list options for the "Size_Selection" to be dependant on the option chosen in "Commodity_Selection".

The options for "Commodity_Selection" are set in 'UserForm Initialize':

Private Sub UserForm_Initialize()
    Commodity_Selection.List = Array("Externals", "Spec Fabs", "Units", "Electronics", "Nacelles")
End Sub

The options for "Size_Selection" are stored in a sheet named "Pick Lists". An example of the relevant workbook sheets is attached below.

Example Workbook for Forum.xlsm

I have tried various solutions involving 'If' and 'Select Case', but none have worked, and I am also very new to using VBA.
Please let me know if you require any more information.

Many thanks in advance for any help!