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Re: REFLECTOR: Nuts, Bolts, & Washers, (oh my!)

On Fri, 23 Oct 1998 07:47:48 -0700 Joe Stack <joestack@technologist.com>
>Hi Folks,
> In talking to various people I've found that many of these, so-called,
expert mechanical >engineers are as lost as me.  Since I generally prefer
to do things the right way I >thought it would be worth spending a few
hours with a good piece of reference >material.

Two guys are partners in a painting business. They have been for several
years but have never worked at the same job sight at the same time.
Things get slow and they land one job of five equally sized rooms in one

They decide to paint two rooms each, then finish the last room. together.
At almost the exact same time they walk into the last room with their
brushes and rollers in hand. But within minutes of starting to paint, one
turns to the other and says "What in the world are you doing!?"

 "What do you mean?" says the other. 

"Everybody knows you paint with a rolled in vertical strokes across a
wall, not horizontally!" says the first.

Fact is, they both were able to paint rooms of equal size with different

Ever hear "there is more than one way to skin a cat!"? It just might be
that your experts and their opinions are all correct in either a general
or specific application.

Rule of thumb in aviation is:  flat washers are used to evenly distribute
torque loads to a surface under a bolt head or screw head and nut. They
should not be considered as a friction bearing surface (i.e. pivot bolts
on the landing gear). Large area flat washers should be used for
retention purposes only. 

Ring or tab type lock washers are used in a torque application, where
internal and external tooth lock washers are used in non-torques
applications where vibration may cause a nut to come off. Nylon inserted
nuts (Esna lock nuts) do not require an internal or external locknut and
should be limited to use in areas where temperatures do not exceed the
ambient temperature by much. (i.e. use of Esna lock nuts on an engine or
many of its components is definitely not a good idea!)

Screw or bolt heads should generally be orientated up, inboard, or
forward. For purely assembly purposes, "all-thread" screws or bolts may
be used. For high stress loads or torque applications, a structural screw
or bolt should be used. Grade (quality) of the bolt depends on the load
and the torque that it will be exposed to.     

Phillips head is much preferred over slot heads in screws. Phillips
provide for a greater torque without "stripping" the head. 

These are "rule of thumb", and as with any rule or rules, there are
exceptions. But this should keep you safe in just about any circumstance.

Safe and Speedy Construction,


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