Simple ring on top of a 3.5 mm audio jack plug for phones and players. Hang a charm, or just use to protect from dirt.
You can even use this to hang your device from a nail, needle, hook or similar. Make sure it fits tightly enough and is pushed all the way in. Note that movement, especially twisting can work the plug out, otherwise tested to support a 200 grams phone.
S size = single
M size = 5 set