In simplest terms, piston rings are thin, circular pieces of metal that fit into grooves in the tops of the pistons.

简单地讲，活塞环就是装在活塞顶部的凹槽里的薄，圆的金属。

youdao

As I said, they make the tops too thin, believing that it is a bigger sound, and they are absolutely wrong.

如我曾经说过的，他们把面板做的太薄，且相信这样会制造出音量更大的吉他，但是他们完全弄错了。

youdao

The air on the tops of high mountains is thin.

高山顶上的空气稀很薄。

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Spires are the thin, pointy tops of buildings.

VOA: special.2010.03.31

In Mr. Drillot's relentlessly harsh lighting, Mr. Lagerfeld's dirndl-waisted skirts (think frumpy gym-class uniforms) and thin tops made both the men's and women's physiques look lumpy.

WSJ: Gambling on Les Ballets de Monte Carlo | Dance Review by Robert Greskovic