axletree vs axle bar

axletree and axle bar both are nouns.

Word	Noun	Adjective	Verb	Adverb
axletree	Yes	No	No	No
axle bar	Yes	No	No	No

As nouns, axle bar is a hyponym of axletree; that is, axle bar is a word with a more specific, narrower meaning than axletree:

axletree: a dead axle on a carriage or wagon that has terminal spindles on which the wheels revolve
axle bar: an iron bar that serves as an axletree

axletree (noun)	axle bar (noun)
a dead axle on a carriage or wagon that has terminal spindles on which the wheels revolve	an iron bar that serves as an axletree