This is a quality marine grade stainless steel (AISI 316) chain specifically cut for anchor chain. The link size is 1/4" or 6.3mm equivalent. Included are two oversized marine grade stainless steel (AISI 316) anchor shackles. Each shackle is 5/16". The total length of chain is 6' measured before the shackles are added. The chain links are made in the US specification style of 1/4" (for the chain link size) and 5/16" (for the shackle size). The Imperial equivalent is generally considered to be 6.3mm for the chain link size. AISI 316 stainless is a premium grade of stainless and is considered by many to be best in class. 316 stainless is corrosion resistant and very durable even in the harshest of conditions.