This 1.3cm g Industrial Strength brand tube plug is made from 316LVM ASTM F-138 implant grade stainless steel. It is hand polished to a mirror finish. Each plug is grooved and comes with two black o-rings. 1-0.3cm through 5.1cm tube plugs are not grooved. The wearable area between the o-rings is 1cm . Sold individually; order two to receive a pair.