I also bought this set exclusively for the keyhole tool. It's actually *almost* too much for what I need. With that in mind, here are the dimensions of the keyhole. large step cuts 7.95 mm or 5/16" wide and 4.1 mm or 5/32" deep. The small step is 4.55mm wide or 5/32 and the edge is 6.1mm deep or 15/64. (The last measurement is the least reliable, but also probably the least important.) I'm pretty sure I want to find a keyhole drill bit that's less than 1/4 inch at its widest point.
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