Harken 16 mm Blocks The 16 mm is Harken's® smallest block. It is perfect for small synthetic control lines found on high-tech dinghies. The patented bearing system uses stainless steel balls in a captive grooved race and has a 250 lb (113 kg) safe working load - the highest on the market compared to similarly sized blocks. The 442 uses a spacer and the 404 uses an )-ring to keep the line in the sheave during intermittent loading. Use for: Dinghy control lines Big Boat leech lines Downhauls Traveler controls Spinnaker pole trip lines Outhauls Cunninghams Halyards on prams