This is for one (1) quality marine grade stainless steel (AISI 316) Straight S Hook 3/16" in diameter. Each hook is stamped 316. The metric equivalent is generally considered to be 5mm. Not to be used for overhead lifting. 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.