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 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. The 567 uses a narrow sheave for extremely small control lines and has a ferrule for soft attachments.