However you may find that a bellhanger's bit works best, they are about 16
inches long, look like a twist drill and have a hole in the tip of the bit
to attach cords or wires so they can be pulled through the hole as you
withdraw the bit. Should be available most anywhere. When sharp they cut
fast and can handle the occasional nail without any problem.
A standard double top plate is 3-3.25" thick in modern construction and no
more than 4-4.5" if built with rough sawn lumber.
I like the auger bits but a cheap spade bit will make a few holes before you
burn it up and will cost about 1/3 the price. The auger bits take a bigger
drill motor so if you are using a 3/8 use the spade bits.
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