5mm wide x 3/8" deep groove This groove works well with doors that use plywood panels.                                                                                                                           You may substitute any of these center groove sets for the standard center groover in the cope & pattern set for free. You may place your order but please specify in a emailor by phone if you choose to substitute. Center groove sets are used with all cope & pattern sets except for passage and entry door sets.                                           3 Wing Cutter