AISI stainless steel 316 provides a long service life that will retain an attractive, clean finish with low maintenance for the discriminating yachtsman Size describes the inside diameter of port hole ATTENTION: 5" Size ONLY features key holes (Key Included). 3", 4", and 6" sizes feature finger holes O-ring rubber seal prevents water penetration through threads Salty Reef Marine Hardware is an American company trusted worldwide for its durability and dependability. The deck port has a secure o-ring in place to keep valuables safe during inclement weather. AISI 316 stainless steel will provide years of service and a bristol shine for the discriminating yachtsman.