ʻO kahi hoʻonohonoho pahu pahu, i kapa pinepine ʻia ʻo "gears," he ʻelua a ʻoi aʻe paha nā pahu pahu pahu me nā niho e hui pū ʻia e hoʻouna i ka neʻe a me ka mana ma waena o nā kumu ʻōwili. He mea koʻikoʻi kēia mau mīkini i nā ʻōnaehana mechanical like ʻole, me nā pahu pahu, nā hoʻoili automotive, nā mīkini ʻenehana, a me nā mea hou aku.
ʻO nā ʻāpana cylindrical gear he mea maʻalahi a koʻikoʻi i loko o kahi ākea o nā ʻōnaehana mechanical, e hāʻawi ana i ka hoʻoili mana kūpono a me ka mana neʻe i nā noi he nui.