I don't have any experience with spline shafts and can't find anything online to help identify this one. It's the input end of a heavy duty hammer drill. 12 tooth. 0.7975" major and 0.672" minor diameter.
It is a common spline drive for hammer drills. You might contact drill bit manufacturers like B&A Manufacturing or Relton to ask if they will share specific dimensional data if that is what you want.