Triple block with 30mm sheave from Allen. It's lightweight and strong, making it ideal for dinghies, windsurfing, kitesurfing, and anything else that uses smaller diameter blocks. Also used on the 420 as a luff block. Triple blocks are typically used in systems such as cunningham or vang, to provide a larger buying system. Bearings: Dynamic blocks feature our patented bearing system which uses two rows of stainless steel ball bearings running on a stainless steel raceway. This provides superior load carrying capacity and longevity over other bearing systems that ride on a plastic rail. Ultra-Strap – Our patented Ultra-Strap is used in our 20, 30 and 40mm Dynamic blocks. The Ultra-Strap is unique from other designs due to its coining process. This process strengthens the band, making it more reliable and durable, as well as making it much more rope-friendly than other designs. The Ultra-Strap was the marine industry's first block designed to specifically work with a rope attachment. Becket - Our 20 and 30mm blocks offer a large center rivet which not only reduces the overall weight but also offers a suitable attachment to the rope, perfect as an anchor point when used in a waterfall system.