Minecraft wiki entry for Lever, associated text: A lever can be attached to the top, side, or bottom of any full solid opaque block (stone, dirt, blocks of gold, etc.), or to the top of an upside-down slab or upside-down stairs (but not to the bottom of a right-side-up slab or stairs). When placed on the top or bottom of a block, the lever orients itself in-line with the placing player.