How to cut space for keyhole hanger without a router?

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keyhole slot bit Keyhole slots are a great way to affix wooden hangings, such as a shelf or picture, to a wall But if the mounting screws aren't perfectly

keyhole slot hanger C , as shown , and for the purpose speci- fied In testimony that I slot , f , in the top , which , in proper How To Make A Keyhole Slot With A Keyhole Router Bit, CNC Router Projects Keyhole