This is a DR Mowball Mow Ball Part Number 311011.
The diameter of this part is 4" and the height is about 3 3/4" .
The center hole is a hex pattern.
This is used on a variety of the DR two wheel walk behind string trimmer mowers.
We have access to many more DR parts, so if you can't find what you are looking for, please feel free to contact us to see if we can list it for you.
Please let us know if you have any further questions!