Ƙungiyoyin ƙwallon ƙafa na matashin kai sun ƙunshi abin da aka saka a cikin gida, wanda za'a iya kulle shi zuwa saman goyan baya. Tubalan Plummer suna ɗaukar tubalan don abin nadi mai daidaita kai ko na ball bearings. An ƙera wannan kewayon don ɗaukar ƙimar mafi girma da matsakaicin gudu da ba da damar tarwatsa igiya ba tare da matsar da hawan mahalli ba.
