16mm 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 250lb (113kg) safe working load - the highest on the market compared to similarly sized blocks.
The 422 uses a spacer and the 404 uses an 0-ring to keep the line in the sheave during intermittent loading. The 467 uses a narrow sheave for extremely small control lines and has a ferrule head for soft attatchments.