This cleverly-designed tool will take care of any problem areas that crop up toward the end of the painting process. Run Block provides three differently contoured aluminum blocks that can be used with wet/dry sandpaper to finish runs that have been cut down with Nib Files. They can also be used for block sanding body filler or primer in hard-to-reach areas. Non-compressible alloy ensures a wave-free finish. Sandpaper not included.