The iboats forum moderators are excited to announce that at this time it appears the iboats forums posting pictures function is working once again. Though we cannot promise for how long, we're hoping for indefinitely.
If you bought it from Iboats it came with the correct hub as a package deal. If you have a mercruiser alpha 1 drive and 3.0L 135 HP engine, according to your link, you would need hub #31.
Otherwise you can use the prop selector to find the right hub.
To order just the hub, you can do a product search for "hub #31" and order one.