Izikrufu ezidityanisiweyo ziyinto eyodwa yoqhagamshelo lomatshini esebenzisa indibaniselwano ekrelekrele yezikrufu kunye nezikhewu ukufezekisa uqhagamshelo oluqinileyo noluthembekileyo. Olu luyilo lwenza isikrufu silungele izicelo ezifuna ukutywinwa okongeziweyo okanye ukufunxa ukothuka.
Kwi-screws edibeneyo, inxalenye edibeneyo ye-screw idibaniswe ne-spacer, engakwazi ukubonelela kuphela amandla okudibanisa okulungileyo, kodwa kunye nokuthintela ngokufanelekileyo ukukhulula kunye nokuwa. Ngelo xesha, ubukho be-spacer bubonelela ngokuzaliswa kwe-gap kunye nokutywinwa kwendawo yokudibanisa, okwandisa ngakumbi ukusetyenziswa kwe-screw.