キャップレス

noun which may take the genitive case particle 'no'

capless; without a cap

Describes items designed without a cap, especially fountain pens, markers, or similar writing instruments.

• この万まん年ねん筆ひつはキャップレスなので、片かた手てで簡かん単たんに使つかえます。

  This fountain pen is capless, so you can use it easily with one hand.