Number + 支 + Noun (long/thin object)
支 (zhī) is a measure word used for long, thin objects such as pens, pencils, arrows, spears, and rifles. In Chinese, the correct classifier must be placed between a number and the noun it quantifies.
请给我两支铅笔。
Qǐng gěi wǒ liǎng zhī qiānbǐ.
Please give me two pencils.
桌上放着一支红色的钢笔。
Zhuō shàng fàng zhe yī zhī hóngsè de gāngbǐ.
There is a red fountain pen on the table.
他买了三支毛笔练书法。
Tā mǎi le sān zhī máobǐ liàn shūfǎ.
He bought three calligraphy brushes to practice calligraphy.