Some of the many versions of the clamp eraser ferrule.
In the animal world there are many entertaining and evocative collective nouns, for example: an army of frogs, a charm of finches, an unkindness of ravens, a business of ferrets, a kettle of hawks, etc. One of my favorites is, a murder of crows.
Of course pencils don’t apply here, but crows have wings that are black. Maybe the usage could be borrowed:
“By the piano were the composer’s only tools: a fresh pot of coffee, and a murder of Blackwings.”