The 15 millimeter edges are my personal favorite to use at the gym, where I still have access to lots of weights, and where the temperature is kept a little too hot to train on the smaller edges.
With exception to the 7 millimeter edges, all the smaller edges are on the slimmest bottom part with only the larger slots at the wider section. This way, there is so excess bulk or material necessary.
Side by side, the original Grindstone (left) and the improved Grindstone Pro (right).
The 7 millimeter edges are one of several improvements between the Grindstone and Grindstone Pro hangboards. This advanced edge is great for hard training or hanging without needing weights.
Notice the asymmetrical, staggered orientation of the edges, keeping your shoulders at the proper (and safe) width regardless of the chosen edge.
The top slot is secure and large enough to fit phones of all kinds. Even larger phones will sit in such a way that they won't fall out.
The phone slot is designed to angle the screen down, making it easy to watch your timer as you grit your teeth and wait for your hang to be done.
As a whole, the board is thin and low profile, making it a great space-saving training option.
Each hold is neatly engraved with the depth for easy reminders while training.
An example of a discounted "cosmetic defect" board, which has minor chips and mars in the wood that don't impede function of the board in the slightest, but will save you money.