pinion and crown wheel vs pinion and ring gear

pinion and crown wheel and pinion and ring gear both are nouns.

Word	Noun	Adjective	Verb	Adverb
pinion and crown wheel	Yes	No	No	No
pinion and ring gear	Yes	No	No	No

As nouns, pinion and crown wheel and pinion and ring gear are synonyms defined as:

pinion and crown wheel and pinion and ring gear: gears that mesh at an angle

Other synonyms of pinion and crown wheel include bevel gear.

pinion and crown wheel (noun)	pinion and ring gear (noun)
gears that mesh at an angle	gears that mesh at an angle