Globally, Stauff clamps represent quick and easy pipe and hose installations, as well as a clean system layout. The vibration and noise reducing features provide and important contribution to environmental protection. Pipe is typically called out by inner diameter size and tube is typically measured by outer diameter size, so be sure to verify the OD of your pipe or tube prior to ordering. The is the the size of the hole in the insert that your clamp will come with. The Nominal pipe/tube size is the size of pipe or tube that will fit that particular clamp. If youre not sure which size you need, please give us a call and we will be happy to help