Where is this sheat from?

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As you can see, my sheath as several small superfacial holls. One is still filled with. Tin ?? Or lead ?? Its only on the front side of the wrangka. I always asked myself of there was a perticuliar meaning for this. Because we are going so deep in this wrangka, maybay someone have some ideas or suggestions. I am not familair with this fenomen in java.