Viadanas sheave boxes are made with Delrin sheaves and Marien grade 316 stainless steel siding. All Viadana products are backed by a 2-year manufacturer warranty against factory defects. Sheave size - 25mm / 1" Max line size - 18mm / 5/16" Breaking Load - 560 kg / 1,234 lbs Base - 47mm x 74mm / 1 55/64" x 2 29/32" Hole Spacing - 57-29mm / 2 1/4" - 1 9/64" Hole Diameter - 5mm / 3/16" Viadana has been in business in Italy since 1961 researching, designing, manufacturing, and marketing nautical products for windsurfs, sailboats, keelboats, and cabin cruisers. Above all, Viadana takes care in using only the best available materials for nautical application, such as stainless steel AISI 316 and AISI 304, aluminum alloys 6063, 6005, 5154, composite fibre, and polymers such as carbon fibre and Delrin. All Viadana products are rigorously tested with laboratory procedures including mechanical tests of tensile strength and chemical salt-proof valuations.