Sub Test()
Dim Plage As Range
Dim Col As Integer, N As Integer
Application.ScreenUpdating = False
Set Plage = Application.InputBox("Sélectionnez la colonne de référence", Type:=8)
Do
Col = Plage.Column + N * 8
N = N + 1
If Col > Columns.Count Then Exit Do
Columns(Col).ColumnWidth = 30
Loop
Application.ScreenUpdating = True
End Sub