There are two standard tripod screw sizes: 3/8"-16 thread-count (smaller) and 1/4"-20 thread-count (larger).
Most small cameras accept a 1/4" diameter, 20 thread-count screw.
Most tripod heads attach to tripod legs with the larger, 3/8" diameter, 16 thread-count screw.
The screw jutting up from your tripod is 3/8", as the Ip*x rotator was designed to be used with professional tripods.
If you go to a well-stocked camera store, you can find an adapter which has a 3/8" female thread on the bottom and a 1/4" male thread on top. If you can find such an adapter, it should sell for a couple of bucks. Unfortunately, these adapters are fairly small in diameter, maybe 3/4", and you may find that your camera is not held all that rigidly on the tripod. Alas.

I heard Remotereality.com might have that part. You can also check with your local camera store.