expansive bit vs expansion bit

expansive bit and expansion bit both are nouns.

Word	Noun	Adjective	Verb	Adverb
expansive bit	Yes	No	No	No
expansion bit	Yes	No	No	No

As nouns, expansive bit and expansion bit are synonyms defined as:

expansive bit and expansion bit: a bit with a cutting blade that can be adjusted to different sizes

expansive bit (noun)	expansion bit (noun)
a bit with a cutting blade that can be adjusted to different sizes	a bit with a cutting blade that can be adjusted to different sizes