A oruka pin ni aaye kan ati ki o ro sinu kan helical apẹrẹ.Eyi jẹ ki ẹrọ ifoso ṣiṣẹ agbara orisun omi laarin ori finnifinni ati sobusitireti, eyiti o ṣetọju ifoso lile lodi si sobusitireti ati okùn boluti lile lodi si nut tabi o tẹle sobusitireti, ṣiṣẹda ija diẹ sii ati resistance si yiyi.Awọn iṣedede to wulo jẹ ASME B18.21.1, DIN 127 B, ati Apapọ Ologun AMẸRIKA NASM 35338 (eyiti o jẹ MS 35338 ati AN-935 tẹlẹ).