This is for two (2) quality marine grade stainless steel (AISI 316) chain snap spring hooks with closed end 1/4". The metric equivalent is generally considered to be 6mm. 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.