Ko te mowhiti o runga me te mowhiti reti o runga kei te hanga i te kowiri tira teitei, he miihini motuhake hei whakarite i te porowhita me te papatahi.
Kua hanga te mowhiti o runga me te whakakai hono pukepuke o runga o-te kounga tiketike he kowiri tira, i te mea rawa machined ki te whakarite roundness me flatness