Forged The beautiful stainless steel shackles we use on Harken� blocks are available separately. We have increased the range in both configurations and sizes. Stamped Shackles The 072, 138, and 246 shackles are used on most of the Small Boat blocks. They are also useful for a wide range of other applications. Snap Shackles The 111, 112, and 1584 snap shackles fit a wide variety of blocks and make them removable. Many use a snap shackle on the lower vang block so that it can be moved from the mastbase to the toerail to use it as a preventer. U-Adaptor The 093 U-adaptor allows blocks with 3/8 in (10 mm) posts to be attached to swivel bases or to other blocks with 3/8 in (10 mm) posts. The 1598 U-adaptor allows blocks with 9/16 in (14 mm) posts to be attached to swivel bases or to other blocks with 9/16 in (14 mm) posts.