替え芯

1. Origins, structure, and basic meaning

• Structure: 替え芯 combines 替え, replacement, with 芯, an inner core. It is read かえしん.
• Basic usage: Use it for refills in writing instruments with replaceable cores, such as pens or mechanical pencils.

2. Common pitfalls and similar expressions

• Pen and pencil refills
  • A pen's 替え芯 is an ink-containing replacement unit, called a “refill” in English.
  • A mechanical pencil's 替え芯 is lead used for replacement or replenishment, called “replacement lead” in English.