E rua ngā momo o te poroporo porowhita:
1) te porowhita porowhita
2) te kakau porotaka kua whakapikohia.
He whānuitia te whakamahinga o te porowhita porowhita i roto i te porowhita, ko te porowhita involute ia e whakamahia ana mō ngā kawenga nui, ā, me tino tika te pokapū me ngā hononga nui. Ko ngā porowhita porowhita he mea whakamahi i roto i ngā waka rererangi, ngā motuka, ngā tarakihana, ngā mahi hanga taputapu mīhini, ngā mīhini ahuwhenua me ngā taputapu tuku mīhini whānui. Nā te mahi maha-niho o te porowhita porowhita, he nui te kaha kawe, he pai te koretake me te arataki pai, ā, ka taea e te pakiaka niho papaku te whakaiti i te kukū o te ahotea. Hei tāpiri, he iti ake te ngoikore o te kaha o te poro me te pokapū o te porowhita, he watea ake te tukatuka, ā, ka taea te whiwhi i te tino tika mā te huri.
Ka whakamahia ngā rakau spline involute mō ngā hononga me ngā kawenga teitei, te tika o te pokapū, me ngā rahi nui. Ko ōna āhuatanga: he involute te kōtaha niho, ā, he kaha radial kei runga i te niho ina utaina, ka taea te mahi i te mahi pokapū aunoa, kia ōrite te kaha o ia niho, kia kaha te kaha me te roa o te ora, he rite te hangarau tukatuka ki te taputapu, ā, he ngāwari ki te whiwhi i te tino tika me te whakawhiti.