The very best screw chuck on the market.  Designed by Jerry Glaser, this versatile chuck allows for three different base sizes.   The sharp steel screw has remarkable holding powers.  No other screw chuck on the market allows such versatility as this chuck.  The three different configurations allow for these different base diameters:   1 1/2", 2 1/2" and 31/2".   The bases are made with a narrow rim rather than a flat surface, which allows better holding strength on non-flat surfaces.   To use, drill a 1/4" pilot hole into the wood blank slightly longer than the thread length of the chuck.  If you need to limit the depth of screw penetration, simply make some thin "washers" from plywood or tempered hard board.  The length of the screw is approximately 3/4". 

 I also have available a wider base that creates an additional two different sized rims.