Some hikers have a favorite trail bottle they're never giving up. The stock cap is the weak link: it's not tethered, and it's usually the first piece to go missing. The Cap & Tether is a 7 g polypropylene upgrade with a TPU tether that stays physically attached to the bottle, so even if you fumble it, it won't end up in a creek. Threads onto any 28 mm bottle (Smartwater, Lifewater, and most narrow-mouth bottles worldwide). It's the same cap and tether system that ships on the NOBO Bottle. A flat silicone gasket sits on the bottle's lip rather than wedging into the neck, so it seals reliably as the bottle ages. Opens with one hand. Works with the Bottle Cap Bidet and the rest of the 28 mm system.