If a coil has no metal core it has an air core.

如果线圈没有金属芯子，它就有一个空气芯子。

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Package type: Cardboard core, or Traverse Wound, or Drop coil.

包装类型：硬纸盒包装或横向缠绕或下行成卷。

youdao

Package type: Cardboard core, or Traverse Wound, or Drop coil.

包装类型：硬纸盒包装或横向缠绕或下行成卷。

youdao