求翻译：龙骨一般选用兴安岭产的落叶松，规格高50mm，宽60mm，长800mm至4000mm，含水率小于18%。辅助龙骨高50mm，宽60mm，长400mm，含水率小于18%。是什么意思？

The keel is generally used Xing'anling production of larch, the specifications of high-50mm, width 60mm, length 800mm to 4000mm, the moisture content of less than 18%. Auxiliary keel 50mm, width 60mm, length 400mm, moisture content of less than 18%.

Keel General Use Xing'an Ling the Larix, standard 50 MM, width 60 mm, length 800MM to 4000MM, less than 18% moisture content. Secondary keel 50 mm high, 60 mm, length 400MM, less than 18% moisture content.

The keel generally selects the larch which Mt. Xingan produces, specification high 50mm, extends 60mm, long 800mm to 4000mm, the moisture content is smaller than 18%.Auxiliary keel high 50mm, extends 60mm, long 400mm, the moisture content is smaller than 18%.

Keel General selection of Larix xinganling etc, high specification 50mm, 60mm wide, long 800mm NM, moisture content is less than 18%. Secondary joist height 50mm, 60mm wide, length 400mm, moisture content is less than 18%.

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