Tylaska Aluminium Halyard Shackle(Special Order Item) Tylaskas halyard shackles have the highest strength to weight ratio of any existing halyard shackle on the market. A captive 17 4PH stainless pin makes for trouble free operation. The all metal machined line thimble allows for use as a 2 1 purchase without the wear or melting that occurs with plastic molded thimbles. Lines can also be permanently spliced for a fixed halyard.