Probably acceptable, in my view. Self tapping screws, by definition, cut their own thread into an undersized hole drilled into the metal. This should ensure a reliable earth connection, perhaps more so than a nut and bolt onto a painted surface.

However I do not much like the particular installation shown, the screws used are too long, and therefore leave an appreciable length protruding into the enclosure, to damage  cable insulation or the hands of a later installer. Use shorter screws, or cut them short with small bolt cutters. 

Probably acceptable, in my view. Self tapping screws, by definition, cut their own thread into an undersized hole drilled into the metal. This should ensure a reliable earth connection, perhaps more so than a nut and bolt onto a painted surface.

However I do not much like the particular installation shown, the screws used are too long, and therefore leave an appreciable length protruding into the enclosure, to damage  cable insulation or the hands of a later installer. Use shorter screws, or cut them short with small bolt cutters. 

Hi broadgage. You make a valid point about self-tapping screws ensuring a reliable earth connection, especially compared to nut-and-bolt setups on painted surfaces. I agree that the thread-cutting action likely provides a solid electrical bond.