Hi Scott, Unfortunately, we do not have that diameter data readily available. But, we can fully guarantee this is a direct fit and compatible with the vehicle application you selected, from 2004 to 2009 Mazda 3 GS/GT/GX/i and S and 4 cyl engine fitment only. The diameter of that balljoint exactly matches the original factory specifications/size/dimension of the factory original of the selected vehicle application. That is why when you have to look up a direct fit part, you will have to enter the accurate year, make, model, submodel and engine size on the selection. As per checking, there is only 1 type of balljoint for the lower for your car(greasable/non-greasable is a common type but less price for the non-greasable).