fountain pen outer cap

例句：

1. 1. The fountain pen is a popular writing instrument.
   钢笔是一种流行的书写工具。
2. 2. The outer cap of the fountain pen is made of plastic.
   钢笔的外盖是用塑料制成的。
3. 3. The writer carefully replaced the outer cap on his fountain pen.
   这位作家小心翼翼地更换了他的钢笔外盖。