With the 'harvestblocks' attribute you can set which blocks you can mine with the item.
Valid values are every integer between 0 and 255 (including both), 'all', 'pickaxewood', 'pickaxestone', 'pickaxeiron', 'pickaxediamond', 'default'. You can set multiple values by separate them with a ','.
Default value: 'default'
harvestblocks="all";
harvestblocks="1,2,3";
harvestblocks="pickaxewood,1,2,3";