On Tue, 24 Apr 2018 03:05:12 +0200, Emanuel Berg
wrote:

Do you need a nut on a bolt's end if the bolt's
direction is down and the hole's walls are
threaded? Could that fail and will it help with
a split washer? For say an M5 bolt, how many
threads/deep hole would one need at the
very least?

The usual rule of thumb is one bolt diameter length of thread is
sufficient as that is enough to provide roughly the same tensile
strength as the bolt shank.

--
Cheers,

John B.