I was building 5/8" slab doors and using concealed hinges. The standard Forstner bit spur left a little pimple on the face of the door and that was not acceptable. But...with the router jig the cup hole for the hinge is completely flat bottomed and utilizing a plunge router, the depth is consistently correct with no overshot possible like with a drill bit. Be sure to use the short collar recommended by the manufacturer. I use POWERTEC 71166 Short Shank Guide Bushing and Nut, 5/8-Inch available on Amazon, as well. The jig is held in place by the hinge screws which are pre-positioned for installation of the hinge when the hole is finished. Some reviewers have said the screw holes do no line up with their hinges, however, I found them to be perfect for my Blum concealed hinges. While setup and the procedure to make the hole is a little more involved, this is a good product and highly recommended for thinner doors especially.