Keep your b.box Sippy Cup v2 leak-proof and ready for use with these two spare silicone O-rings. Designed specifically for the b.box sippy cup, these durable rings provide a secure seal to prevent spills. Easy to insert, simply hold the O-ring in the lid??s rim and carefully run your finger around it to ensure a tight fit??avoiding sharp objects that could damage the ring. Once in place, screw the base back on, and your cup is good to go!