[TowerTalk] Shackles, Thimbles and Big-Grips

[Frank Donovan]

Hi J.P.

I've never had a good quality 3/8" galvanized steel anchor shackle fail on
an AB-105 tower in 25 years, including a 125 MPH microburst.  The size
you decide to use depends on how conservative you want to be...

The "safe working load" is permanently marked on almost any good
quality shackle. For example, the "safe working load" of a 3/8" shackle is
2000 pounds, a 7/16 is shackle is 3000 pounds, a 1/2" shackle is 4000
pounds and a 5/8" shackle is 6500 pounds.  However, the "proof load" is
2.2 times the "safe working load," and the "minimum ultimate strength" is
six times the "safe working load."  

The pin diameter of various shackles is:
3/8"  shackle: 7/16"
7/16" shackle: 1/2"
1/2"  shackle: 5/8"
5/8"  shackle: 3/4"

If you are  V E R Y  conservative, you might want to use a 5/8" shackle,
and I do use some of these, but for the most part I'm using 3/8" shackles.
You can drill the guy attachment plates for AB-105 if you need
somewhat more clearance.  The steel used in AB-105 corrodes very slowly,
so you need not worry about that issue (I drilled some of mine 25 years
ago with no apparent degradation.)

The Big-Grips are designed to work with 502 insulators.  Just pass them
thru the holes in the insualtors and begin the crossover at the second set
of paint marks. 

73!
Frank
W3LPL
donovanf@sgate.com


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