Neither Robert Dyas nor my local hardware store have screws that fit the keyholes on the back of the Desktop Pi case. No 6 screws (5/8th inch) are the smallest in stock at both places and they don't fit through the 0.254 inch hole in the back plate. The hole is too small AND the hole has insufficient depth.
My box is now nicely wall mounted because I drilled out the hole and removed the plastic that restricted its depth. Consider either making a fairly ordinary keyhole shaped hole in the back or including two screws that fit the existing mounting holes.
Consider, also, allowing the user to remove and re-fit the centre ring so that the word Element 14 is horizontal rather than vertical after wall mounting. It looks like it might be possible, but the lugs might break so I won't chance it.