Qhov sib luag sib luag yog ib hom yeeb nkab hla, sib luag sib luag txhais tau tias tag nrho 4 qhov kawg ntawm tus ntoo khaub lig nyob hauv tib lub taub.
Tus ntoo khaub lig txo qis kuj yog hu ua cov yeeb nkab sib txawv, nws yog cov yeeb nkab hla uas plaub ceg kawg tsis nyob hauv tib diameters.
