knob vs knobble

knob and knobble both are nouns.

Word	Noun	Adjective	Verb	Adverb
knob	Yes	No	No	No
knobble	Yes	No	No	No

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

Other hyponyms of knob include nailhead.

knob (noun)	knobble (noun)
a round handle	a small knob
a circular rounded projection or protuberance
an ornament in the shape of a ball on the hilt of a sword or dagger
any thickened enlargement