The 16 mm is Harken’s® smallest block. It is perfect for small synthetic control lines found on high-tech dinghies including Optimists (Optipart number EX1334). The patented bearing system uses stainless steel balls in a captive grooved race and has a 250 lb (113 kg) maximum working load. The 404 uses an O-ring to keep the line in the sheave during intermittent loading.