Normally the threads are cut from the size stock indicated, so they should
be a bit higher than 1/4" on the wood screw side, almost 1/4 on the machine
screw side. With a full set of bits, you should be able to go 1/16 less and
have plenty of hold. I like to sight the shank of the drill versus the body
of the bolt for appropriateness.

Don't use soap to lube screws, it's deliquescent, and will promote
corrosion. Traditional is wax. Beeswax or paraffin canning wax would
work. Oil would soften the area, which is opposite of what you want.

"Bart V" wrote in message
...
I need to drill a couple of holes to screw a 1/4" hanger bolt into the
heel of the neck (jatoba) so I can bolt it onto the pot/rim (also
jatoba) I turned on the lathe. I'm wondering what size drill bit to
use, something around 7/16" fit the bill, or that too big? I'm only
getting one shot at it else the neck for the banjo I'm making is toast
and I don't wanna screw it up at the last minute...
Also wondering if, before screwing in the hanger bolt, soaking the
drilled holes with oil would make the wood stronger?
Graciously looking forward to a hint or two,