They are called tether handles. You are right, they absolutely keep your fingers safe.
The guy I got them from doesn’t appear to have a website anymore. With that said, I now make my own 1/8” Amsteel dogbones.
Here’s how I do it:
1: Start with 24” piece of 1/8” Amsteel
2: Taper both ends (that’s 6 stands since 1/8” is a 12 strand weave)
3: Mark each end at 6” and go to the middle of the strand with your tool (loop turner/bent over wire) and fish to that 6” mark
4: Bury that end back until you have about a 1” loop (I pull the loop over a regular sized Sharpie) and it works well.
5: Repeat steps 3 and 4 for other end
6: Optional, but I run a 7” length of shock cord through each side to act as a limiter for how wide the handles will stretch as you are advancing using them. It’s just kind of inefficient if you allow them to completely flatten. This also prevents the loops from pulling out since I don’t make these with a locked Brummell splice. Side note; a straight eye splice like I do here is much stronger than a Brummell splice. .
Edit:
If you use bigger diameter rope for your top tether, just leave your loops a little bigger. I sometimes use 10.5mm Platinum as my top tether and made those loops a little bigger.