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Explanation: To the To the government and Ernst gives the folllwiung translations for "Dorn":
Dorn m (jeder Art, z.B.: Aufweit-, Richt-, Spann-, Ziehdorn) (Wzm) / mandrel, mandril (GB), arbor (US)
Dorn, Stachel m / spike, thorn
Dorn, Zapfen m / gudgeon
Dorn, Durchschlag m (Werkz) / drift
Dorn, Kernstab m (Schweiß) / core rod
It seems as they might be referring to is a spike or other tool, used for punturing steel drums or tins.