The drill was used to add detail to the clothing, usually the tool is used to provide a stating point for the channeling tool to add depth. In this case, as is typical of 15th century practice, the drill has been used without the channeling tool.
Notes
The unfinished tableau created for the coronation of Ferdinand II of Argon by Benedetto da Maiano was intended for the Porta Capuana in Naples. The hands in this example are not fully worked in the round.