It turns out that the 3M 400 grit ("extra fine") sponges are not much different than these 400 grit ones.

I could easily differentiate the four coarsest and the four finest grit, leaving the four medium grit by process of elimination

I especially appreciate that they stamp the grit on the end of the block, because without that it's difficult to tell the difference.

Previous reviewers have complained that these sponges were not labelled and/or that they appeared to actually be in a much coarser grit range.

The grits are inaccurate and it has loose material that scars the wood, I only recommend this to sand the walls or when you only want to remove the top layer.

Love the different grits

Revised, works great 180 grit cuts like 100 grit.

However, I won't have any use for these for a while since I was expecting to be able to use the 4 finer grits (300+).

I got no fine or superfine grits

Sanding with water is most often done while sanding automotive type of painting and using grits finer than these pads are sold in, like 600 git to 1600 and finer black paper