I purchased this item after measuring an existing tap connector. When this new one arrived it was way to big. I now have them side-by-side: my old connector measures 1" internal diameter; the new connector measures 1.25" internal diameter. The box it comes in is however labelled 1". If you read other reviews you can see other people have had the same problem. The supplier assures me this is correct so please beware, you need to be a plumber in order to understand the measurements for this product.