Spheres are super classic!
They are versatile in that they can train both the open handed strength (when hung from above to do pull ups) and pinch strength (when grabbing the sphere straight on).
Different sizes add diversity to your training. Larger spheres will require more wrist strength, whereas smaller spheres focus more on fingers.
Make sure to grab them in pairs if you want to do pull ups!
By default, spheres come with a standard loop, but an insert variation can be requested for those wishing to fix these to their open-top loading pins.
Larger spheres (8" and 12") can be special ordered.