They use a step out bit, the same one that an electrician uses to make various size holes for electrical conduits.
It basically looks like a small top with various steps or widths. The smallest width is probably a 1/2 inch and it steps out at roughly 1/4 inch increments.
They carefully center it over the bolt they want to expose and keep drilling until the diameter is the size they need.
Of course they have to hold the frame guard away from the frame as they drill.
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Steve Berkner
I've attended 21 Six Days as a working Photojournalist
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