I'm not sure what inside diameter you are asking for, but if you are referring to the shaft size, it is: 1/2". Here is a link to a dimensional drawing image and our sheave page. Let us know if you need any more info. http://www.e-rigging.com/Sheaves-and-Pulleys http://www.e-rigging.com/assets/images/Drawings/GBP/sheave_specs.jpg