This is for two (2) high quality marine grade stainless steel (AISI 316) main support ring clasp. The size is 8 mm or 5/16" nominal. Not used for overhead lifting. AISI 316 is a premium grade made of stainless steel and is considered the best of its class. 316 stainless steel is corrosion resistant and very long durability even under the toughest conditions.