crosspiece vs crossbar

crosspiece and crossbar both are nouns.

Word	Noun	Adjective	Verb	Adverb
crosspiece	Yes	No	No	No
crossbar	Yes	No	No	No

As nouns, crossbar is a hyponym of crosspiece; that is, crossbar is a word with a more specific, narrower meaning than crosspiece:

Other hyponyms of crosspiece include rundle, rung, spoke, round, rung, stave, cross thwart, thwart, transom, traverse.

crosspiece (noun)	crossbar (noun)
a transverse brace	long thin horizontal crosspiece between two vertical posts
a horizontal beam that extends across something	game equipment consisting of a horizontal bar to be jumped or vaulted over
	a horizontal bar that goes across something