57mm Carbo Ratchamatic Block by Harken

Uses: ILCA and Optimist Mainsheet. Composite fiber-reinforced sideplates, hardcoat-anodized aluminum sheave, a lightweight soft-attach, and a minimum of moving parts in the ratcheting mechanism.

The Harken ratchamatic features an automatic ratchet system which engages when the block is under enough load. This means that when sailing downwind, the ratchet does not engage until the wind gets over 10 knots, which allows for more fluid sheet control in light wind conditions.