Abstract: A centering jig assembly for centering guide holes for a drill provides an improved adjustment feature, which avoids reliance on fasteners to fix the position of the screw device with respect to the clamp jaws. The jig assembly includes a first holding element having a first threaded bore extending therethrough and a first bearing face bearing against a first engagement surface of a work piece and a second holding plate member having a second bearing surface and a second bore extending therethrough for alignment with the first bore, the second bearing surface bearing against a second engagement surface of the work piece. A center axis of the first bore and a center axis of the second bore are collinear defining an axis of travel. The first and second plates are adapted to translate generally parallel with respect to each other along the axis of travel.