Hey Bryan,
Ken is right. They have a fairly short life-cycle. The failure of one can be devastating.
We put carabiners on some older ones and use them for tie-backs or strain reliefs.
Most I donate to my local wrecker buddy or my 4x4 friends when their "time" is up.
They all have serial numbers and we track and records are kept on their entire life span.
I've replaced almost all my poly core with the new SteelTex steel core.
I've watched them do failure testing on both types at the SpanSet facility here in town. It's about 2 miles from my shop. They are fantastic people.
The poly core slings just go "pop" and the mandrels continue apart, the SteelTex put up a mean fight and go down swinging.
Only about half the diameter of the round sling does most of the work, the remainder of the material in the load radius is in compression and is unable to carry load. I think the little 1/16" steel wires in the SteelTex sling flatten a good bit and put more material to work because the sling gets pretty wide when the tension hits it in those tests.
VERY impressive to watch that pressure gauge go to 20,000 lbs. and that round sling
hold that force in check. Thats almost 4x what it's rated at!
I'm a SpanSet dealer. PM me. I can get you what you need on the down-low.
When you see them build them, you know who to trust................
Dan 0;)