I've you've never used a single point rifle sling, the sling webbing usually connects to a loop adapter on the rifle. The webbing is typically 1-1/4" give or take a 1/4".
Here's another example of a single point sling:
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The above photo is the Specter Gear MOUT sling and I have a couple of these (one on an AR-15 16" Carbine variant and a Remington 870).
The Remington 870 has a single point sling attachment plate. This is the exact one I use:
So you'd pretty much need something that will take 1-1/4" webbing (or whatever width the sling is) and mount that in the tripod screw of the camera.