The door is to be centered in the door seal piece so the door will fill the hole cut for it which makes the inside smooth.

大门是要集中在门密封件等的大门，将填补这个洞的削减使内部顺利。

youdao

The shell is smooth on the inside.

贝壳内壁光滑。

《牛津词典》

The coat was smooth and shiny inside like her sister Sylvia's blouses.

外套里面光滑发亮，就像她姐姐西尔维亚的衬衫。

youdao

So far, I have found it incredibly smooth to drive, powerful and roomy inside.

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Inside, the tunnel was cool and dark, about thirty feet high, with a smooth ceiling, faintly lit by work lights along the edges.

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