These single flare plugs are made of obsidian, and come with “O” rings for securing them in place. Popular choice due to their rich, black color that can be used in everyday wear and go with anything. Smooth and polished. Sold in pairs. The plugs are available in any of the following sizes / gauges: 8 gauge (3.2mm), 6 gauge (4mm), 4 gauge (5mm), 2 gauge (6mm), 0 gauge (8mm), 9mm, 00 gauge (10mm), 7/16" (11mm), 1/2" (12mm), 9/16" (14mm), 5/8" (16mm).