The boom block with becket is attached to the aft end of the ILCA boom. Pass your mainsheet through the block, down to the traveler block, and back up to secure to the becket. This is the latest ball bearing version from Harken as included on all new ILCA boom assemblies. A great upgrade for an older boat, particularly for light air sailing! Attaches to the boom with the stainless boom block eyestrap (sold separately).