I was trying to get my son excited about gripping his pencil properly, as opposed to from the very end, but wasn't having much luck. He's big into animals, especially sharks at the moment, so I modelled a grip and replaced the central ‘barrel’ that wrapped around the pencil with this incredible shark model by Geoffro.
I modified the shark by straightening it out to align with a pencil, removing the smaller fins, elongating the torso, and adjusting the proportions to suit the application. The central hole through the shark is modelled with a 7.5mm internal diameter and should fit most pencils, but your mileage may vary depending on pencil dimensions. Feel free to experiment with scaling it to suit your writing utensils.
Note: This prints with supports due to the orientation and it might take a little effort to free the finger holsters.