counterbore vs countersink bit

counterbore and countersink bit both are nouns.

Word	Noun	Adjective	Verb	Adverb
counterbore	Yes	No	No	No
countersink bit	Yes	No	No	No

As nouns, counterbore and countersink bit are synonyms defined as:

counterbore and countersink bit: a bit for enlarging the upper part of a hole

Other synonyms of counterbore include countersink.

counterbore (noun)	countersink bit (noun)
a bit for enlarging the upper part of a hole	a bit for enlarging the upper part of a hole