The Allen 30mm Dynamic Block Back To Back is a versatile and reliable choice for various applications such as triangle backstay systems found on sports boats and dual pole and spinnaker launcher systems like those on a 49er. Its patented dynamic bearing technology, featuring twin rows of stainless-steel ball bearings on a stainless-steel rail, allows for a superior load-carrying capacity and durability compared to other bearing systems on plastic rails. The block consists of two opposing sheaves held together by a strong stainless steel side strap and nylon mouldings, ensuring it can handle high opposing loads without separating. Its design also allows for maximum control with two lines running at up to 180 degrees to each other.