Isiqukathi iyunithi yokupakisha impahla ejwayelekile esetshenziselwa ukuthutha impahla. Ivamise ukwenziwa ngensimbi, insimbi noma i-aluminium futhi inosayizi ojwayelekile kanye nesakhiwo ukuze kube lula ukudluliswa phakathi kwezindlela ezahlukene zokuthutha, njengemikhumbi yezimpahla, izitimela namaloli. Usayizi ojwayelekile wesiqukathi ungamafidi angu-20 namafidi angu-40 ubude namafidi angu-8 no-6 ukuphakama.