The keyway needs to be 14mm wide and 4.5 deep. The widest tool I have for the shaper is 12mm. So that will mean at least two goes at it. Would it be better for me to use an 8mm wide cutter whereas I have to set it over anyway? Or center the 12mm cutter and then skim each side or take one 12mm cut and set it over 2mm to bring it to dimension?.. Helical gear shaper cutters are mainly manufactured to customers specific requirements, especially in the form of single helical cutters. MORE INFO. Extended Back Boss Type Gear Shaper Cutters. The extended back boss type cutter is designed to avoid the problems associated with obstructions on the work piece preventing full working movement. MORE INFO.