Breaking Strength of Aluminum Clips for Trim Chains

Load Lab
Test Results - Breaking Strength of Casted Aluminum Clips for Trim Chain

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Created by Delbert L. Hall, Ph.D.
ETCP Certified Rigger - Theatre and ETCP Recognized Trainer

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Disclaimer: This site contains the currents results of ongoing research and is not a finished presentation of findings. The information on this site may be the results of a small sample of tests and are NOT conclusive evidence of anything – they are just my results. Take them for what they are. Any conclusions drawn from these results are yours and not are necessarily mine. Go the Load Lab Home to read the complete disclaimer.

Although rated anchor shackles and quick links are the typically used today for terminating trim chains back to the thimble, not too many years ago the industry standard was to use casted aluminum clips (aka dog clips) for this purpose. There may still be thousands of theatres which still use these unrated clips in their counterweight rigging. The goal of this test is to determine the breaking strength of these clips.

The clips used in this test are ones that I recently removed from a theatre after approximately 30 years of service. The clips all appeared to be in good condition before the test.

Date of test: January 22, 2009
Item: Cast Aluminum Clips
Rated Breaking Strength: ??? lbs

Sample # Breaking Strength (lbs)
1 540
2 578
3 584
4 527
5 590
6 559
7 570

High: 590 lbs.
Low: 527 lbs.
Mean: 564 lbs.
Median: 570 lbs.

All the clips broke in the same location.

Once a design factor is applied, the rating of these clips would be extremely low for stage rigging. I recommend that these clips be replaced with properly rated hardware.