It’s a beautiful thing… The love between a yo-yoer and his string :
Man as soon as my lathe comes in it’s strings schmings.
To answer the op’s question, that is a swivel that you can get in the fishing department of your local walmart, fleet farm, etc. On the end of that is a paperclip or similar hook… Make sure you get yourself some quality $5-10 swivels, not the cheap ones. Get Spro swivels. They are the best. I use them and only them for fishing and it is worth it!
Spro swivels are great for wireline connections. 
yes they are