This is a 120mm diffused downstem from Gear Premium, the part that carries smoke from the bowl down into the water. The diffuser end has slits that break the smoke into smaller bubbles, which cools it and smooths the draw compared with a plain open-ended stem. The colour-changing glass shifts tone as it's used, a nice touch on a part that's usually plain. Check your bong's joint size and the length you need before buying, since a downstem has to match the piece. A good swap if your current stem is plain or broken.