The jig can be mounted to a substrate or clamped directly to a workpiece; it works the same either way. The jig lacks any type of adjustment for different workpiece thickness: You drill the same hole spacing (1" on center) unless you reposition the jig for each hole. And the thumbscrew "clamp" requires lots of turns when going from a thin board to a thick one, and if you overtighten it you'll likely leave a dimple on the wood. There are no markings on the jig for lining up on a workpiece, so you have to eyeball it. The included drill bit dulled quicker than all the others, resulting in tear-out around the pocket holes.