Question regarding wire rope thimbles

[GBtimex]

Dear Riggers,

I was hanging some on stage monitors the other day when I came across a problem.

The wire rope thimbles I had bought for our 1/4" air craft cable were painfully narrow. We could not get our shackle pins through the eye of the thimble and had to attach them to an eye bold instead. While this solution actually worked better because we ended up attaching a turnbuckle so we could then make the exact adjustment that we needed for the speakers; it did get me thinking.

Was there a wider thimble that I could use that would be safe for overhead rigging? My supplier had no other selection in stock at the time. I checked my handy Crosby catalog and it was reveled that a "open pattern, hot dipped galvanized steel" was available for sale. Item G-408 for those of you in the know.

I thought I would ask you wiser rigging folks for your thoughts on the matter. I am planning on buying them but if they are unsafe or just not worth getting then I will pass.

Thanks so much,

GBTimex

 

[Footer]

How small were the thimbles and what sized shackle were you using? A 5/16" shackle is usually what is used for 1/4" cable.

 

[GBtimex]

Sorry I miss spoke,

The shackle pin DID fit but that was the only thing that would fit. I could not get either the I bolt going into the speaker (factory size and style of course) or the thimble into the Bell of the shackle. The part of the shackle that takes in the pin was too wide to fit past. I believe it would have fit had the thimble itself been wider.

Does this clear things up a bit?

GBTimex

 

[Footer]

Once again, what sized shackle were you using? Rigging hardware tends to be sized so that gear if similar SWL tends to fit together nicely.

 

[MPowers]

Sounds like you were not using a 1/4" thimble or not using a 5/16" or smaller shackle. I just walked out to the shop and put a 5/16" shackle easily through both a 3/16" and a 1/4" standard duty thimble. Check your actual size against the tables shown here.
VER SALES, INC. - Thimbles
Shackle Specs
Any 1/4" thimble will accept a 1/4" or 5/16" shackle. A 1/4" shackle is by far the most common size shackle for theatrical use with 1/4" wire rope. It is the size recommended by JR Clancy, SECOA, H&H et. al., the size they supply with the rigging systems we install, the size on their pre-assembled trim chains, etc. 5/16" Shackle is the second most common, usually spec'd along with SECOA STC chain or JRC Alpha Chain. When architects spec the higher duty chain and the larger shackle, it is usually changed when several of the potential rigging contractors submit Product Substitution Requests pointing out that the 3/8" chain (1250# WLL - double wrapped 4:1 design factor x 2 = 10,000# breaking strength) and 1/4" shackle (1,000# or 1/2 T WLL - 5:1 design factor CM or 6:1 Crosby x 2 = 10,000-12,000#) are stronger than the 1/4" wire rope, ( 875# WLL - 8:1 design factor = 7000). The times 2 on the chain and shackle ratings are because the chain in a basket configuration imparts only 1/2 the total load on each side, i.e. the load is evenly divided between the attached end of the chain and the free end with the shackle. NOTE: If the system design involves a straight, inline connection from the lift line, such as a chain or turn buckle attached to the end of the wire rope line on one end and to a batten clamp on the other, without wrapping around the pipe, then each element in the system carries the full load.

As for safety, any proper sized thimble will handle your load. Thimbles are not rated in terms of load capacity, they are rated for light, standard and heavy duty for gauging the resistance to wear from various friction, load shifting, side loading, etc., conditions that are rare in stage rigging, somewhat more common in arena and outdoor rigging and quite common in construction rigging. For 99% of indoor stage rigging, a standard duty thimble is fine.

 

[tprewitt]

I think I see what you are getting at - the thimble would not fit in the eye bolt on the speaker? If all is wrong is the opening at the top isn't big enough simply bend it open a little (twisting sideways is easier than opening up like a clam.) insert it, then bend it back. This is fine as long as you don't kink or really misshape the thimble. You have to do the same to get it in a link of chain.

The G-408 is opened for you. I'd have to read the documentation to be 100% positive but I'm pretty sure Crosby says to bend them closed. If you don't, either the clips or nico will be too loose and the thimble could fall out or the wire rope will be bent at a sharp angle.

The thimble, must be appropriately sized and the the eye bolt should not be so small as to put pressure on the sides of the thimble (in a wedging action.)

In the end it sounds like you did a much better thing. I try not to make points without a shackle or turnbuckle or something to undo them. Everything has to come down someday.

-Ty