I had my head in and was about to open the lantern, when my finger slid on a piece of metal and made a noise.

VOA: special.2009.05.16

So, the active part of the thermometer could be water. It could be alcohol, mercury, it could be a piece of metal.

那么温度计的工作部分,可以是水可以是酒精，水银，可以是一块金属。

麻省理工公开课 - 热力学与动力学课程节选

With this method,the printmaker cuts or etches an image onto a piece of metal.

VOA: special.2009.09.02

Near the trees he saw a shining piece of metal.

VOA: special.2010.03.20