Reef block, sheave 90, SWL 8.000 kg. The blocks are connected to the leech of the mainsail with webbing, and reduce point loading on the mainsail when reefing. The small diameter sheaves are suitable to very high loads. The center hole can be used as a safety connection to the boom when reefed.
The small version (D=50 mm) is for boats to 50 ft, larger (D=120 mm) for boats to 100 ft.