Umklamo usekelwe ku-geometry yama-engeli alungile nama-arcs.Ifomu lesimanje, elivumelanayo lihlaba umxhwele ngemininingwane ecwengisiswe ngokuphelele, futhi umxube obekwe odongeni, ne-spout yawo ebheke phambili kancane, ikhiqiza kabusha i-engeli lapho amanzi avela khona.