Do17 or Mustang?

A piece from the wing of a Do17 or P51 Mustang?
Can anyone familiar with the (wing) construction of these two aircraft types identify which one it is likely to come from please? No, it has not come from the Goodwins, and before trying Cosford (where staff are rather busy at present), it would be helpful to have a yes or no to the possibility of it being Mustang.
Approx dimensions of the top hat (bowler hat?) stringer/stiffener are as follows:
‘hat’ height 0.85″ (21mm)
‘hat’ base width 0.6″ (15mm)
overall base width 1.6″ (40mm)
Rivet heads are flush on the opposite side of the skin to the stringer/stiffener

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