This clever design holds the clew of the sail onto the boom of your Topper® or RS Tera. The velcro has a locking strap (nominal 40mm dia.) to prevent accidental removal. The webbing is an expensive spectra webbing so that it slips nicely along the boom. (38mm dia. boom). Class legal (Topper) complete with a retaining line, It can be tied off to the sail clew eye to prevent loss.