[SEL] Semi-OT: Flats & bevels on nuts

Richard Allen linstrum55 at yahoo.com
Wed Mar 23 12:41:00 PST 2005


Usually the flat, or flattest, bearing end of a nut faces or goes in
contact with whatever it is holding. This is because nuts need as much
contact as possible to distribute the pressure over the greatest area
possible, which keeps the pressure-bearing surface from becoming
distorted. If it gets distorted, then the last part of the thread where
it emerges from the inside of the nut may get damaged, with the
consequence that the bolt or stud thread may get badly torn up when the
nut is removed, or make getting it off very difficult. Sometimes the
bevels on the very tips of the wrench flats get machined so that they
extend too far into the pressure-bearing surface of the nut. This is
because the operators who maintain the nut making machines don’t do a
very good job of adjusting the cutting tools when the machines are
maintained. Some of you may remember my rant about commercially made
pipefittings, which suffer from the same improper machine set-up. With
nuts, if a lock washer is used (which is usually the case), then it is
a moot point which way the nut faces, but just as long as the flat is
wider than the lock washer. If you look at a lock washer you will see
that there is a bevel on its inside edges so that they do not bear on
the last part of the thread where it emerges from the nut. Despite this
feature, lock washers quite often have their chisel points angled so
that they chew up the thread on the nut anyway, but at least it usually
does not cause any harm because metal is removed rather than getting
mashed into the thread groove. The reasons why the tips of the wrench
flats are machined on a bevel are to facilitate getting box and socket
wrenches onto the nut as well as to keep from tearing up the mechanic’s
fingers and knuckles. At least in theory! I have worked on a lot of
machines that had sharp-edges on the nuts and bolt heads and they just
tore my fingertips to pieces.

Work and play safely!


Rich

~:/+\:~:/+\:~:/+\:~:/+\:~:/+\:~:/+\:~:/+\:~:/+\:~:/+\:~:/+\:



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