50mm Double Dynamic Block With Becket.The A2053 is a high performing ball bearing block, designed to eliminate friction and allow rope to run at great speeds. Ideal for use on Keelboats and Catamarans for a range of applications from jib sheet to mainsheet systems, to backstay tensioning systems and everything in between. The 50mm double is a great choice for systems which require a larger purchase system with minimal friction. Bearings Ð Dynamic Blocks feature our patented bearing system which uses twin rows of stainless-steel ball bearings running on a stainless-steel rail. This provides a superior load-carrying ability and longevity when compared to other bearing systems available on the market.Swivel Lock - The A2053 comes with a removable swivel lock moulding. When installed, the shackle can be locked in 90-degree orientations. When removed, the attachment shackle can spin freely. Becket Ð This pulley features a central becket between the sheaves. This allows for easy termination of a rope as well as helping keep the load centralised.