I-unit yokubamba-okubhujiswa (ekhulunywa njengoba "umshini wokubhujiswa okubhujiswa") kuyindlela entsha yokubhujiswa ethembisa ukufaneleka okuphelele kwezindawo zesitripi, okwenza kube nomdlandla wemishini yokubhujiswa kanye nomshini wokubamba-okubhujiswa. Izimo zakhe zezokusebenza kuyinto ukuthi isitripi isenza ukunyakaza okuphazamiseka phakathi kwesitshini sokubamba nokubhujiswa kwesikhala kanye nesitshini sokubamba esinendawo yokubamba okuhambisanayo nokubhujiswa okuncane okuncane. Kuyakwazi ukuthuthukisa izifo zezigaba ezintathu zesitripi, njengoba isitshini esinendawo, isitshini sokugcina nokubamba okuhambisanayo, kanye nokubamba okuncane, kanye nokwethula okuphazamiseka kwesigaba.