No room for two sheaves side by side so these twinned ones were designed. The install like the pair on the left. The two in the middle show the captive Torlon ball track on two sides of one twin, but only on one side of the other with a partial track its mate runs in. Antal tulip on the right. These fit in the same space but with no intervening cheek. So fairleads are required to keep them from jumping the groove.