Question: Can we use 2 slings linked by a shackle to strangle a steel stick?
Answer: When connecting two slings together, shackles are the preferred method. When connecting slings using shackles be sure to follow the following steps.
1. Prevent shackles from eccentrically loading (pulling at an angle). If this is not possible shackle rating should be reduced for the application.
2. Prevent shackles from pinching the sling between itself and the load. This can cause damage to the sling, shackle or load.
3. Prevent the eye of the shackle pin from binding into the load.
4. When multiple slings are loaded on one end of the shackle, it must be the bow end. The pin side is designed for inline loading only. Having two slings pulling at a given angle from the pin side of the shackle compromises its rating and performance.
I have redrawn your examples plus one. Your drawing of the double wrap rendered choker hitch with a shackle has the orientation of the shackle incorrect, whether by design or accident I’m not sure. However, I have added an additional drawing indicating the correct orientation of the shackle.