Variable rowsource for Combobox

Please see attached workbook for a sample.

So on Sheet4 column A there is a list of materials which will be variable.
I want to use that list as an input for the combobox on the userform.

Tried makeing it variable like this (and other ways) but without luck :

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Could somebody please set me back on track again?

Superb again Norie!
That did the trick, thanks.