COSTA SILICONE RETAINER: Flexible, durable and lightweight, the Costa Bowline retainer is a streamlined silicone retainer with sliding bead for adjustable tension to make sure your sunglasses stay put, on and off the water. From end-to-end, the Costa Bowline Silicone Retainer measures 19". The Costa Bowline Silicone Retainer is compatible with all Costa sunglasses. VISIT THE COSTA BRAND SHOP: Click on the Costa logo above to view the entire Costa sunglasses and accessories assortment.