Commercial Level Urethane Pro Style Dumbbells.
Pro Style Dumbbells compact the weight of the dumbbell closer to the wrist of the user, allowing greater range of motion and a much easier lever-effect on the wrist.  

30mm handle
up to 32mm in larger sized.
Embossed logo

 Thick, high-quality urethane coating is inert, with no offgassing and nearly indestructible.