Kumashafti okukhanya okunemba, ngokuvamile kunezidingo zokuqina kwendawo.Inhloso yobulukhuni bendawo yangaphandle ukuthuthukisa ukumelana nokugqoka.Ngezinto zensimbi, ukuqina kokuqina, ukumelana nokugqoka.Kodwa-ke, lapho umnyombo uqina, ukuqina kokuqina, kanye nokunciphisa ukuthwala nokumelana nomthelela.Ngakho-ke, ngezidingo ezibalulekile ze-shaft: ubulukhuni bangaphandle kanye nokuqina kwangaphakathi.