This is for one (1) quality marine grade stainless steel (AISI 316) spring hooks forged 5/16". Each spring hook is laser etched 316 with the makers mark. The forged spring hooks are made in the US specification style of 5/16". The Metric equivalent is generally considered to be 8mm. 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.