No Measuring Needed to Mark Keyhole Slot Fastener Locations on

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You could mill a wide horizontal slot at the base of the vertical keyhole, that way two screws can be 'incorrect Infinity Cutting Tools - Keyhole and T-Slot Router Bits More Info:

magic 27 slot Use this handy bit for flush mounting pictures, plaques, clocks or small cabinets Bit bores an entry hole, then cuts a 316 slot to secure a screw or nail How To DesignMake Keyhole Slots for CNC Router Projects