This is for two (2) quality marine grade stainless steel (AISI 316) spring hooks 5/16". Each spring hook is stamped 316 and laser etched 5/16" with the makers mark. The spring hooks are marked 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.