Harken 3.00 in (76 mm) Blocks The 3.00 in (76 mm) single block comes in high-load or low-load configurations. High-load blocks feature Torlon® bearings and forged stainless steel shackles. The wire version features Hardkote-anodized, Teflon®-impregnated aluminum sheaves for strength and corrosion resistance. Use for: Main and jib sheets Spinnaker halyards Control lines