Hi Tim, Mark --
My understanding was that a properly-chosen thimble (correct
diameter, correct shape of the groove, and correct wall thickness) will
maintain the shape of the loop under all load conditions up to failure.
There is no need to use a 504 insulator.
The "Handbook of Rigging for Construction and Industrial Operations"
is an excellent reference for this kind of work.
As Tim mentioned, the WIRE ROPE thimble groove's side walls are an
important part of the system in forming an eye: the walls and groove
work together to support the preform (in this case) around the curve,
keeping the cross-section of the preform round and distributing its load
evenly to the thimble. A thimble that has a too-big groove will cause
the load to deform the preform, weakening the system. A thimble with a
too-narrow groove won't allow the preform to seat properly. And a
thimble with thin walls will distort under load. See
for an example. Use the correct size for the diameter of the preform.
Once the eyes are prepared with correct thimbles, the "Handbook"
states three options for connecting the eyes together:
a) shackle: It is important that the load be centered on the
shackle; otherwise the shackle's capacity is reduced. The best shackle
for this job is a "chain shackle" (shaped like a D, with the pin forming
the vertical part of the D). One thimble will pass around the pin, and
the other thimble will nestle in the curve of the D. The chain shackle
is better than an anchor shackle (bow shaped) for this purpose because
it maintains the straight alignment. Washers may be used to keep the
thimble centered; e.g., centered on the pin. Here is an example:
b) mechanical connecting link: See
for an example. Do not use the pear-shaped links, as the load can shift
out of straight-line alignment. Use the regular link.
c) turnbuckle: Use a jaw-jaw turnbuckle of appropriate load
This would be a possible approach at the transition at the bottom of the
buy. A turnbuckle 8-10 feet above the ground can be accessed by step
ladder for adjusting guy tension, and is less likely to be vandalized.
(However I don't bother with turnbuckles on tower guys.)
Not mentioned in the "Handbook" is the twin clevis link, an example
of which is here:
This would be my preferred solution if a turnbuckle is not needed. The
two pins go through the two thimbles, and the pins are safety-wired in
place. Use washers if required to keep the thimbles centered on the pins.
-- Eric K3NA
on 2010 Jul 23 10:57 Tim Duffy K3LR said the following:
> Hello Mark,
> I have had good success with a 502 insulator - to make the Phillystran to
> EHS transition. I think the 502 is a safer route than shackles and thimbles
> that might cause either preform (Phillystran or EHS sides) to distort over
> 73 and be safe,
> Tim K3LR
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org] On Behalf Of Mark Robinson
> Sent: Friday, July 23, 2010 9:43 AM
> To: TowerTalk@contesting.com
> Subject: [TowerTalk] Joining Phillystran and EHS
> I am getting ready to assemble the top guys on my rohn 45 tower. I intend to
> use a short length of 1/4ehs at the top and maybe 27 feet of 1/4 ehs at the
> bottom. I will be using a length of Phillystran HTP667001 in the middle. I
> will use the PLP2755 big grip on the philly with a 1/2 inch thimble. I will
> be using a BG2144 big grip on the 1/4 ehs together with a 3/8 thimble. My
> question is how to join the ehs and the philly together. Can I just use the
> two thimbles looped inside of each other at the joint or do I need a shackle
> or maybe a 502 insulator between the two big grips.
> The shackle would need to be fairly substantial to have a working load near
> to that of the cable at 6000 pounds. How have other people made this
> 73 Mark N1UK
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