This is for two (2) quality marine grade stainless steel (AISI 316) 5/16" UNC (approx 8mm) hook bolts. Each bolt is stamped with the grade of 316 and the makers mark. 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.