Knucklebones are a delightfully simple skill toy that can be manipulated with the fingers to create smooth rolls, flips, and dexterous tricks. This KBone is a 3D-printed version designed for satisfying hand feel, balanced weight, and everyday carry. Its curved shape fits naturally between the fingers, making it perfect for fidgeting, practicing coordination, or learning new tricks. Durable, lightweight, and easy to pick up but challenging to master, the KBone is a small object that rewards skill and creativity with every move. 

Here is a video demonstrating the Knucklebone by the company that invented them

Knucklebone Introduction - Aroundsquare - YouTube

If you like this model check out their selection of premium knucklebones and other skill toys. I personaly own a couple of their KBones and I use this 3D printed one for when dropping my nice ones could result in damage or loss.

This KBone can be sanded and polished for an extra smooth feel but honestly it works great as is. 

Although sometimes the parts may seem to hold together very well this model is designed to be glued together with superglue.