Leaky nibs in Angela's Ashes

The headmaster, Mr Scallan, says we are to return on Monday with a composition book, a pencil, and a pen with a good nib on it.

There are seven masters in Leamy's National School and they all have leather straps, canes, blackthorn sticks. ... They hit you if you're late, if you have a leaky nib on your pen, if you laugh, if you talk, and if you don't know things.
Frank McCourt, Angela's Ashes, 1996