It looks like an external hex implant. There are 12 notches, but that's a trick to maximize positioning flexibility. Look at Brånemark System (Nobel),Biomet 3i and Steri-oss to see if it matches. Pay attention to the height of the hex as well.
How deep is the hex...here is a guide to the three external hex's brane, 3i, biohorizons- this will show you the measurements of the hex which will help you determine which one it is... and if you need parts for any of them we have them....