48x48px textures aren't possible best to my knowledge, they have to be powers of two. Because there is no such thing as half a pixel.
That's just how it works.
Unless Minecraft automatically sterches the textures into the nearest possible power of two, in wich case making 48x instead of 64x would be pretty pointless, as the textures would be sterched anyways.
48x48 means that each default minecraft pixel is 3 x 3 pixel grid, so it should render fine.
And my brick 48x texture:
48x48 means that each default minecraft pixel is 3 x 3 pixel grid, so it should render fine.
Very nicely done
Meh, meh...