Simply straddle the board between the pins and cut your mortise – perfectly centered every time! Plate is constructed of 1/4" Acrylic with 1-1/2" opening, and is transparent for visibility. Solid brass guides thread easily into 3 different insert settings for a variety of wood thicknesses and for non-centered mortises. Predrilled hole pattern fits: Porter Cable 690/890 series, Makita 1100-1101 series, Bosch 1617-1618 (fixed base only) and Dewalt DW616/DW618. 6-1/2" diameter. 11/16"L guide posts.