[TowerTalk] Nuts & Bolts

[k3fy at arrl.net]

Which is better for the hardware to hold together the legs of my aluminum
tower sections?
Galvanized or Stainless steel?  

    I prefer Stainless Steel but you must use Anti-Seize Paste on the threads as stainless will gall at times without it.  Keep in mind the bolts will be in a shear type application and that the aluminum will be the weak link here.  A standard 18-8 stainless fastener will have more than enough strength.


Finer thread (3/8-24) or courser thread (3/8-16)?   
    For this application it makes no difference.  Fine threads are generally not available in galvanized as the threads would be easily clogged during the galvanizing process.  Stainless is available in the finer thread but not as commonly available and hence they can be pricey.

    But, what would improve your bolted joint is to buy the bolts so that the shank (unthreaded portion) will protrude completely through the joint in question.  (just a minimum amount) This helps in several ways.
1. No threads will be in the joint to dig into the metal if any movement occurs.  (especially important on aluminum joints)
2. Improves the shear strength of the bolted joint.  

    You will need to use two to four flat washers plus a lockwasher to allow the nut to tighten without running out of threads.  Keep in mind that all nuts have an internal chamfer which will allow a little extra tightening before it bottoms out.


 Flat washers plus lock washers and standard nuts? or flat washers and
locknuts? 
    I use a flat washer, lockwasher and nut.  A lock nut is not really needed in this application but if you want to use one you will need the nylon insert style to work well with the stainless bolts.  

    A point of information on galvanized fasteners:  Most galvanized fasteners are still hot dip galvanized.  Galvanized nuts are tapped oversize before galvanizing to allow for the increase in the pitch diameter of the threads due to the zinc coating.  No such adjustments are made to the bolts.   Therefore a proper fit is only assured when both the bolt and the nut are hot dip galvanized.   Lock nuts are generally not used with galvanized fasteners.  The galvanized coating has a higher rotational friction.  This along with a lockwasher is usually more than enough.  Special styles of lock nuts are available for use with galvanized fasteners when needed. 


Mark Holzbach K3FY

Mark 


    



I use 
If Locknuts, should I use the nylon insert type or the type with the indent?

Advice appreciated....  Jerry K3BZ