Otu mgbanaka kewara n'otu ebe wee gbadaa n'ụdị helical.Nke a na-eme ka onye na-asa ihe na-agbanye ike mmiri n'etiti isi ihe nkedo na mkpụrụ, nke na-eme ka igwe na-asa ahụ sie ike megide mkpụrụ osisi na eriri nke bolt na-emegide akị ma ọ bụ eriri mkpụrụ, na-eme ka esemokwu na iguzogide ntụgharị.Ụkpụrụ ndị ọdabara bụ ASME B18.21.1, DIN 127 B, na United States Military Standard NASM 35338 (nke bụbu MS 35338 na AN-935).